UE4 Editor crashes after using the 'Play' function - Signal 11 Linux

The file that you attached appear to just be the crash report and callstack, There is no project attached. As far as reproducing the issue, I’m still not sure what you mean by “uncomment the UMG line in the C# file to use UMG source”. What C# file are you referring to and what UMG are you referring to? If you can reproduce this in a new project, please zip the project folder and attach it.