I think I have just figured out what caused the problem for me after about 6 months of pain!
Just now I started doing some clearing up of all the error messages and warnings I was getting in the Output Log and once that was all pretty much cleared up the Print (to screen) messages all started to appear again!
I’m wondering if there’s some kind of limit I was hitting where all my errors and warnings were blocking up the Print printing? That might be something for other people to check too if other things don’t work.
Reset to defaults is greyed out and none of the other solutions fixed it for me. Rather frustrating.
Where do you locate UnrealEngine.cpp?
This worked for me. Some of you might be having this issue because you used the ‘DisableAllScreenMessages’ command at some point. I did what @wixz said and it solved the issue for me.
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Yeah, I had disable all screen messages set in the level bp on begin play that I forgot about cause I was taking screen shots and didn’t want to re-bake lighting. 
For those who still can’t find a fix - check your fonts in Project Settings. I have messed with them, changed the default fonts to ones i later removed, and the prints stopped working. Just set them to the default Roboto (if you can navigate the ContentBrowser to them), or any font you want, restart the project et voila!
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Try delete folders: “intermediate” and “saved” and open project again.
I’m do this and printstring working now.
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Thanks, WixZ! I had used a DisableAllScreenMessages command in the game mode, to disable errors about lighting needing to be rebuilt. It would run every time the game was launched. Had forgot to delete that command. The command will persist, unless EnableAllScreenMessages is typed into a command prompt (can use “`” in the editor to enter it).
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This is how the issue got fixed. Just make sure you run it before your need to run the Print String command.
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I just ran into this issue, but for me it was easily fixed by re-enabling Show Stats.
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Thank you! This actually fixed my issue as well. Deleted all logs and restarted the editor.
in my case, restarting UE4 fixed it.
This worked for me. Apparently Shift-L turns off Stats which I didn’t realize. Must have hit it by mistake.
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Thanks for this! Fixed for my project.
Thanks! It worked for me. I forgot I disabled all screen messages a long time ago.
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This solved my problem. Super easy fix. The default for console commands is the ` key. Then paste in “EnableAllScreenMessages” and press enter. Worked in that test and subsequent tests, even after toggling on/off ai debug visuals with the ’ key.
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Thanks a lot!!! your solution worked for me
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ENABLEALLSCREENMESSAGES worked for me
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Using 5.3.1, had the same problem after using the AI debugger. Typing ENABLEALLSCREENMESSAGES into the console worked!
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