Explicitly calling
filebot --license will do the trick in most cases, but on Synology NAS the license key path is shared across for all user accounts, while license activation status is specific to each user account, so you may need to
filebot --license once for each user account.
On Synology NAS, each
$USER will has it's own FileBot application data folder and caches and so
filebot --license and
-clear-cache work only within the context of the current calling
$USER, and thus can only fix license activation status for the current calling
$USER due to file permissions.
On Synology NAS, the easiest way to reset everything is to just
uninstall the FileBot package completely via Synology DSM. That will clear all FileBot application data for all users.