Dear Arduino Team,
I use 2.0.0 beta 4 for my current development.
I cannot reproduce the issue with sistematically steps, but it happened to me several times.
I did a lot of works, edit files, complie and upload and all il fine.
When I reopen the sketch It seems that I lost of my last development itereation and I need to search in user Temp folder for the last version of my sketch.
Now I check the timestamp and content of the file and when there are no matches I need to save with Ide a copy with another name.
Edit - I just download Beta 5, I will check this issue with new version and I will give feedback...