Hi,
Just as a quick sanity check, and because this is so strange to have occurred with no changes to the project or environment, have you deleted the following folders in the project before attempting to regenerate project files:
- .vs and/or .idea
- Binaries
- Intermediate
- Saved
- The solution file itself
You can also safely delete the Build and DerivedDataCache folders, but these really shouldn’t affect the project in this kind of way.
Thanks,
Hayden