Step 1 - Check Vimeo video status here - If the status is "operational", then the issue is from your internet connection.
Step 2 - Try any of the below tips and tricks to resolve your issue.
✅ Log out completely and open a new web browser; log back in.
✅ Refresh your browser and install any updates
✅ Clear browser history / web caches and log back in to your account
✅ Close excess browser tabs or applications
✅ Turn off WiFi from your phone and try to access the videos using your phone data
✅ Try from a different web browser (safari, chrome, etc)
✅ Try from a different device