Incremental Sync Cache Size clearing

The system just look the size of cache that holds the new configuration, if it is above the value you sent in "maximum Incremental Sync size" it will do a full sync. At the end of a successful sync, it should just clear the cache and start over.

Look the ltm logs /var/log/ltm you can see the reason for the failure. Probably you just started to sync when a sync was already in process.