Welcome to the community...
It looks like your project got corrupted somehow
You might want to restart using your latest backup...
Why backups are important see also here MIT App Inventor 2 Tips – TWO DOG APPS
Did you save a Project file (aia) to your computer or save a copy of your Project as another name? If you did not, what you coded in your situation is probably corrupted and unrecoverable as was indicated by Taifun.