Zyxel 5398, RILCMD error: CREG_INTERNAL_REG_DENIED what this line means?

With each IP change forced by the internet provider, unless manually rebooted, the modem, while correctly receiving the lease of the new IP, fails to automatically reset the new IP received at devices already connected, instead providing them with a RILCMD error: CREG_INTERNAL_REG_DENIED

Im getting these disconnections on a daily basis, im getting insane lmao, seem that i cant find any solutions to this issue. bought the router 1 year ago, didnt had any problems..everything started at the end of March 2024.

attached the log,

if someone could help me please :))