RouterOS hot-spot problems.

Hi everybody, i have a RouterOS v5.8 (upgrade from 5.6) with a hot-spot.
Sometimes some users cant get access to the hot-spot routeros page though they get ip by DHCP (172.16.0.0/24 subnet, gateway = 172.16.0.254).
If I input other ip manually, then 172.16.0.254 open normally.
I suppose, that something is blocking these users.
After reboot all work great.
How can i fix it?
P.S. on 5.6 i also have this problem.