Presumably because of a change in the WS library for FLEx, it is now the case that we can't start Solid if there are any .ldml files in the folder:

C:\ProgramData\SIL\WritingSystemRepository\3

Well, for some users the crash only happens if there are writing systems with names that are too long, or have variant modifier tags that are too long. For me, it happens if there are any .ldml files. The workaround is that we make sure FLEx is closed, and we delete all the files in this folder, and then start Solid.

If we try to start it we get a crash. I'll paste the crash report into a comment.

I don't know if anyone uses the writing system capability in Solid at the moment.