Please run housekeeping on your database via 'Database -> Database Management'. Click the 'Housekeeping' button and run the following in this order:
1. Reindex
2. Cluster
3. Vacuum/Analyze
If that doesn't fix it then please
enable logging, reproduce this problem in your screenshot and then send your log file to us in a
Support Ticket along with a
database backup. You will need to upload the backup to cloud storage (Dropbox, Google Drive, etc) and share the link in the ticket - do not post the link here to keep it private. If you do not have any cloud storage just open the ticket with your log file and we will send you instructions on how you can send us your backup.