I am working on a file, which is not my own and therefore cannot be posted -- and it is a really complicated one. This file, when loaded into Blender 2.81 crashes blender sooner or later. I inspected the crash-files and enabled debug mode and found some hints here and there. I want to recreate the problem with a newly created file, which I can post. But before reporting, I want to make sure, that I am not reporting something, which cannot work. The file was initially created with Blender 2.79 and still works with Blender 2.80. Loaded into Blender 2.81 it crashes Blender after a short time or freezes it. What kind of compatibility is intended between these three versions of Blender? (I know, that 2.81 is in its early stage... )
If it crashes then it's a bug. Please report it on the bug tracker (Help > Report a Bug in Blender). It would be ideal if you can create a .blend file that can be shared publicly.
You should be able to open and run 2.79 files in newer version with the exception of removed features such BGE or the Blender Internal render engine which no longer exist in 2.8 and beyond.