PfSense box hangs after some time

[aileron]

Hi folks!
I have witnessed some really strange behavior on my network lately. After having worked flawlessly for about 3 months, my pfSense box (one of these Celeron Mini-PCs with 4 interfaces) suddenly hung. I was not even able to restart the box, it just did not boot. So I decided to connect one of my 4G wireless modems (some ZTE device) directly to the network to maintain Internet connectivity for the network. It did not take long before it failed. I could restart this box, but it kept on hanging. I sent it to the manufacturer for service and got a (completely different) wireless router as a temporary replacement. Funnily enought, this one keeps failing as well, I have to reboot it at least once a day.

Meanwhile, I figured out that my pfSense box runs without any problem when it is not connected to the network. Once I connect it, it hangs again after some time (several minutes to several hours). And I need to wait some minutes before I can even successfully boot it again. (This, again, is only when the box is connected to the network.)

All these devices, including pfSense, were configured for IP 192.168.0.1 which is the network's gateway. I start to believe that the problem lies somewhere within the network, maybe there is something like a DOS attack going on even though I generally trust everybody on the network. Almost nobody on the network has the technical skills to execute such an attack, but maybe someone connected an unsecured WiFi box or something like that.

Has anyone ever had similar problems on their networks? Or anything I could try?

What I will do today is connect my notebook computer as the network's gateway and use pcap/Wireshark to monitor traffic. Anyone has any further suggestions on what to try/check for?