NAS326, problem with access, UPnP get back OFF after some time

Hi everyone,

From time to time I lose an access to my NAS from the Internet. It still works fine from LAN. When I'm checkin the status in mycloud.zyxel.com I can see all services have UPnP disabled. It looks like this

Then I anable some services e.g. like below,

save it and it works a few weeks, month maybe and then agin become unreachable.

NAS is connected through the UPC Horizon router. It has fixed IP in LAN.

Does anybody meet such a problem before ? Any ideas?

Thanks