I had to replace my previous Hitron modem and Rogers store gave me this modem 3553. I have noticed that it starts rejecting login to admin pager 4 or 5 days after reboot. It still works fine but I cannot login to admin page anymore. It stops loading the signon page.
I've come across customers experiencing similar issues, but never the short time span you are. From my experience it sometimes locks up and is in need of a power cycle after a few weeks, but never a few days.
Can you verify which firmware your modem is currently running on? It may be in need of an update.
If anyone else in the Community is reporting a similar issue, please feel free to chime in.
I think I got this modem in late August. I have sent PM to the moderator to include me for the beta formware updates. So hopefully, I should get formware update very soon. 5G range is pathatic. My modem/router is on the ground floor but at the back of the home and I don't get signal in the front room on the second floor.