Is this happening within your modeler?
I know this seems redundant, but have you tried:
A) Sign out and then back into Mendix?
B) Restarting your computer?
C) uninstalling and reinstalling Mendix?
What you can try is to delete the local project folder.
Usually you can find that folder in: C:\Users\User\Documents\Mendix\
Then re-download the project from the Mendix portal.
Make sure you save/commit your unsaved work.
Let me know if that helps!
Could you try to open the app from the project page in the Mendix portal?
1. Go to https://sprintr.home.mendix.com
2. Open your project
3. Use the 'Edit' -> 'Edit in Desktop Modeler' option on the top right.