yes maybe there’s a bug in that cache. The code is here: https://github.com/xwiki-contrib/application-glossary/blob/master/application-glossary-api/src/main/java/org/xwiki/contrib/glossary/internal/DefaultGlossaryCache.java and used in https://github.com/xwiki-contrib/application-glossary/blob/master/application-glossary-api/src/main/java/org/xwiki/contrib/glossary/internal/GlossaryTransformation.java
There’s probably no logs unless there’s an un unexpected error. If the problem is a logic error in the code we won’t see anything in logs. The code at https://github.com/xwiki-contrib/application-glossary/blob/master/application-glossary-api/src/main/java/org/xwiki/contrib/glossary/internal/GlossaryTransformation.java and https://github.com/xwiki-contrib/application-glossary/blob/master/application-glossary-api/src/main/java/org/xwiki/contrib/glossary/internal/DefaultGlossaryCache.java doesn’t seem to log anything.
Yes I would suggest to read the code I linked above. I could help if you can find a way to reproduce the problem on a clean XS install so that I can reproduce.