The logs do not reveal much. Over the span of 4 logged hours, data connection was stable. Signal metrics are decent as well. The logs, however, are annoyingly flooded with DHCP requests from some TP - Link device. Would it be possible to configure a static lease for it in an attempt to avoid these messages?
For further troubleshooting, I would suggest to monitor whether the router has mobile connectivity at the moment 404 pages start popping up. One of your screenshots does indicate disconnects, would be interesting to check if the behavior is related. It would also be good to use the device with a single SIM as WAN, not in load balancing, for a while, to find if your connectivity issues are related to a certain operator or they happen regardless of the operator.
I would then need you to generate and attach a new troubleshoot file, soon after the issues with website access occurs.