Title says it all really. Sometimes, mostly after an upgrade in my experience, I will go to edit a View that uses CiviCRM Custom Fields and will find messages like 'broken handlers' etc. How can I fix this?
In most cases this is fixed by running
drush cc all. I don't know what the circumstances are that causes the upgrading 'clear caches' to not suffice but this seems to be the fix.
If 'Clear Caches' does not suffice you could also try Structure > Views > Settings > Advanced, Clear Views' cache but I have never needed to do that.