From time to time (mainly while checkout out git branches with a lot of breaking changes), some classes are indicated as non-existent. "Check for external changes", mvn clean install of the multiple-module project etc. all don't help. 

In this bug occurence today, we had to remove the cache and restart Netbeans. The classes that went missing were generated classes in a dependency (jpa metamodel). When viewing the dependency in the project where the problem occured, we could find the classes reported as missing by Netbeans. Editing / saving the classes to force a recompilation didn't help (it sometimes does).

How to force the cache to be updated? Would there be some way to tell how it became corrupted? We can take additional metrics next time.