ZW USG 1100 don't release DHCP adresses

Yes I am see that as said here https://community.zyxel.com/en/discussion/comment/47756/#Comment_47756

Also there is a slight behaviour difference between V5.35 and V4.73 where V5.35 an expired IP does get removed from the table the time for this to happen seems to be 6 hours but seems to reset if you login to the zywall.

As for why alexey is not seeing the reuse of expired IP's to new clients could be a bug in a large Subnet with lots of clients and how the Zywall handles this situation might be the reason for the problem.