I'm getting the error "connected but no internet" or "internet not available". After restarting the modem everything works fine again but usually after a few days to a week I'm getting the same issue

It's a student housing with 12 rooms. It's annoying cause I have to go there and restart the modem every time. I thought the issue could be that there are too many devices connected to the network. However currently there are only 3 rooms occupied.

Setup is like this

Ground floor

AP1  -> AP2 -> switch -> modem

First floor

AP3 -> AP4 -> switch -> modem

The problem is not the ISP, on the modem and switch all the lights are green. When I connect to the wifi from the modem/router it does connect.

-4x TP link Archer AX12

-They are all in AP mode

-DHPC is disabled on all AP's

-I used wifi analyzer app and chose the best wifi channel for each AP, before this it was set on automatic

-I changed the DNS on the modem to google's DNS

-Lease time mode is 24 hours

-I changed the firewall on the modem from high to medium

Really hope someone can help me out