As the old licensing concept is mainly based on counting of database sessions (and not on actively retrieving/returning license tokens), the surrender of seats automatically works well if a session is terminated abnormally, or the database crashes, and so on.
For the new licensing concept, a synchronization mechanism was allotted:
A purge/scavenge-task works in the background. It checks the sessions and compares them to what is indicated to be reserved from ISL. If a seat is found to be reserved from ISL, but has no related valid session in the database, the software will surrender the seat to ISL. If the surrender fails, it is tried next time of clean-up.
Do not delete rows from license seat tables manually or update them in some way,
because the clean-up job may not return the seats to the license machine and they
remain reserved from ISL "forever".