Unknown Cook Failure after migrating to 5.5

Development Programming & Scripting
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1

I have a build of my game on 5.4.4 that works perfectly fine and builds fine as well. After hearing about 5.5’s fps improvements I made a 5.5 copy. This copy refuses to build always giving an Unknown Cook Failure. I went through the logs and found that almost all of my downloaded items from Fab had errors associated with the materials instances:
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The weird thing is that the default material the Fab assets use is in the engine and works perfectly fine:

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image1889×380 118 KB

Regardless, I swapped out all the Fab MI’s with my own MasterMaterial MI’s and it got rid of the yellow errors. However, I’m still getting the Unknown Cook Failure and now I suspect it has to do with the huge walls of VirtualTexture errors:

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image998×305 61.2 KB

I turned off VT’s a while ago in 5.4 and never had any trouble building. Could it be something else in the log that I’m missing? Here’s the full log:
SubTerraUE554_2.log (355.9 KB)

2

Hi,

Hope you’re doing well!

Try to reaload the textures before cooking.
Filter all textures then Right Click> Asset Actions > Reload Assets.

Then try to cook again.

Hope that helps - take care.

3

Thanks for the advice! I went through my entire project and reloaded each texture. A lot of them said VT yet when I dragged one the VT would go away… Unfortunately I’m still having the Unknown Cook Failure with the wall of VT errors even after this.

I’ve also started seeing these specific lines popping up in the output log:

[2025.07.18-22.02.56:165][709]UATHelper: Packaging (Windows): UbaSessionServer - Delaying 1 processes from spawning due to memory pressure (Available: 8.3gb Total: 55.8gb)
[2025.07.18-22.02.56:165][709]UATHelper: Packaging (Windows): UbaSessionServer - NOTE - To mitigate this spawn delay it is recommended to make page file larger until you don't see these messages again (Or reduce number of max parallel processes)
[2025.07.18-22.02.56:165][709]UATHelper: Packaging (Windows): UbaSessionServer -        Set max page file to a large number (like 128gb). It will not use disk space unless you actually start using that amount of committed memory
[2025.07.18-22.02.56:165][709]UATHelper: Packaging (Windows): UbaSessionServer -        Also note, this is "committed" memory. Not memory in use. So you necessarily don't need more physical memory
[2025.07.18-22.02.56:165][709]UATHelper: Packaging (Windows): UbaSessionServer -   MaxPage:   4.3gb
[2025.07.18-22.02.56:165][709]UATHelper: Packaging (Windows): UbaSessionServer -   TotalPhys: 51.5gb

I have no clue what this means or why it’s just now popping up. I restarted my computer and built again to no avail. Here’s the new log:
SubTerraUE554.log (656.0 KB)

4

Ended up solving the problem. I went through each and every folder validating until I found a warning saying the lights had no Mipmap levels and were related to the VirtualTexture0 errors. Turns out I had some lights in one of my levels that needed to be rebuilt. I ended up just rebuilding the lighting for the entire level and it seemed to fix it. Really wish UE would’ve told me what the log was referencing :confused: