This happens to me quite frequently. I'm not sure what causes this issue but here are some things that seemed to help fix it for me:
- Disable antiviruses or adblockers for Construct and make sure Construct has all necessary permissions
- Check if your computer has a low amount of storage space
- Clear your cache and cookies
- Try opening the project on a different device
- Try saving the project as a local save if you're using cloud saves
I hope these can help.