did you managed to fix it? Sorry, but I do not understand the solution. 
For me this turned out to be a Cinema Camera. I basically moved all the contents into separate sub-levels and saved them off until I found the objects that were causing the lock-up on save. I deleted the cameras and everything is saving fine now.
Sorry for the late answer.
Yes, we fixed it by forcing an update/compilation of the different master materials that we use.
Since then, no more bug 
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How do you do that exactly? I am using 5.3.1 at the moment
I have figured out a relative cause of this issue and how I fixed it with me. Many people here have suggested it is materials related AND IT IS. tl;dr Check all blueprints for invalid nodes that have invalid material references (probably a material you were recently working with) by trying to compile them. UE5 wont tell you theres a compilation error (in this case) if the blueprint isnt pulled up. Dont just refresh the node. Delete it and make a new one.
I was following a tutorial for how to drag and drop in-game, and got to the end and everything was working great. I thought I would stop for the night so I closed UE5. I accidently clicked that I didnt want to save changes that I made to a material I was using for Drag and Drop. After that, my UE5 froze while trying to save. Stuck at 75%. When I tried to load back up the game, I had to go way back in the tutorial because the whole drag and drop system was broken. It was saying my DD blueprint was invalid. I kept trying to refresh the node and it made the blueprint appear like it compiled successfully but every time I went to save it would freeze at 50%. But when I Deleted the node for the DD blueprint, everything worked great!! I made a brand new node for the DD and it still worked perfect. If I didnt have the Blueprint pulled up that had the issue with the DD blueprint, then UE5 never told me anything was wrong. But the moment I pulled up the BP that used the DD blueprint, it refused to let me compile because of the issue with the DD blueprint nodes. At itās core the fix occured because the reference to the material was corrected. It was trying to save an invalid reference to the material which was causing it to freeze!
Iām just adding on as well, getting this error and have been unable to find a solution. I hope this issue gets addressed soon!
(UE v5.3) I ended up finding a solve for myself after a few hours of messing around. So for me, this problem seemed to be caused by a master material that was the parent of a lot of different instanced materials. Specifically when I had brought in multiple assets from SpeedTree. What I had to do in order to solve the issue was find the master material from speed tree that was connected to the instanced materials, then open it up and disconnect the output of the Substrate Legacy Conversion node from the āfront materialā of the final material output. After disconnecting it, I saved the material even with the errors it gave me, then I waited for the new shaders to compile. After this, I reconnected the Substrate Legacy Conversion output to the āfront materialā, and then saved once again.
If I recall correctly, this totally solved the issue, I canāt remember if I had to restart the program after this, but I donāt think so.
So in conclusion, it appears this whole issue was caused by some sort of corruption in the SpeedTree Master Material. I have no idea though and Iām not going to pretend I understand whatās going on under the hood of Unreal. I saw some other people in this thread mentioning that they used a similar solve for this but it was a specific blueprint that needed to be recompiled or deleted, or to force an update of a certain material. Iām not exactly sure though what they mean about āforcing an updateā.
I really hope this explanation at least guides someone in the right direction, but Iām really not sure as this issue was very nonsensical and really quite a detrimental bug in the program, especially since there was no crash log.
Letās pray this issue doesnāt make it into further updates!
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I get this issue also just trying to save a new material instance created from one master material, tried resaving the master no go, it seems to be a memory leak as GPU memory slowly keeps growing if you leave it on the freeze.
I fixed it by moving my master to use material attributes.
Forcing the parent material to recompile has been fixing the issue for me and it has been happening with materials that are already using attributes.
Are you sure it wasnāt more that you forced a recompile?
Happens to me too. Disconnecting something in a master material and forcing it to recompile that way often fixes it for a while. It happens once or twice a day though while weāre importing stuff left and right and creating many materials (like 50-100 a day). Didnāt use to happen on 5.1, but has happened with 5.3 4 times so far in the last 3 days
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hell yea that solved it
wasted hours upon hours of our coders and tech guysā¦ we went through the whole engine code but without success
but apparently klicking one single button fixes all of your struggle
thanks
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Thanks, updating the master material solved the issue for me
Hello All,
Could you please describe a little more what/how the issue was solved? I have the same problem with UE 5.3 and for now I could solve it with switch from directx 12 to 11. Now everything works fine, but after I switch back to dx12 and try to save freeze happens again.
I would like to use the displacement feature, but it only works with dx12.
Thanks a lot!
Same issue here when using material instances.
Problem was that inside the master material the texture u coordinate was multiplied by a scalar parameter which was accidentely set to zero as default.
After setting it back to ā1ā the saving worked as usual.
I tired to check all the Master materials, but I cannot find any issue like that until now. I also downloaded a UE5 project with few things in it, opened in UE5.3 and it crash also when I use dx12.
Weāve been having the same problem for two weeks or so. Seems to be card specific, our 3090s all have the issue but our guys with 4090s seem to be unaffected.
Solved: We just ran a quick Redirector Cleanup on the content folder, no one seems to have had the issue for a few hours now. Iāll update if it becomes a problem again.
We have the same issue too. I have a 3080 and we have a master materials with many (1000s) of instances from it. We are not using Nanite or Lumen or anything like that. It does usually save eventually but can take maybe 40 minutes or so. I am wondering if itās recompiling all the shaders but thereās no feedback about what itās doing. Right now I am trying to save a new material instance, texture and simple model. Sometimes itās jsut fine saving and other times it stalls like this.
Having the same problem. Solution is not working for me. It is a real bug. UE please fix. Impossible to work like this. Wasting time.
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Same problem here. Project worked last time I ran it. Now it freezes if I try to save or add variable to level blueprint. I tried the āFix redirectorsā on my content folder, and then it removed my mapā¦ 
Specs: AMD Ryzen 9 5900X, NVIDIA RTX 3080 Ti and 64GB of memory. Nothing peaks or anything.
Alright, I seem to have found out what caused my issue. I had two paragon characters and I tried to merge them together (share the Global folder instead of having a seperate for each character due to alot of duplicates), by doing āReplace referenceā from one character to another. Reverting these changes brought my project back. So itās probably something with material instances/master materials as stated above.
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Specs: AMD Ryzen 9 7950X, NVIDIA RTX 4090 and 128GB of memory
When I make any changes to the material, even the most minor ones, and when I try to save the material, the project freezes at 0%. The next time I re-enter the project, I open the parent material, disable any node, save it. Then I plug it back in and save it again. After that, I can make changes to the child materials for a while and safely save them. And this happens until the project freezes again. And then I repeat the manipulations with the mother material. I understand that this is the wrong way and the error lies somewhere deep in unreal, but it works for me.
PS This happens when using any materials. So the problem is definitely not the material.