Jumbo frames? https://en.m.wikipedia.org/wiki/Jumbo_frame
I haven't enabled jumbo frames knowingly on my system, but even if I had, why would the issue occur only every few weeks? Also, it seems to be rather independent of the actual network load.
A friend had networked speakers that would freeze until a manual reboot time to time. It turned out to be the Linux running within the speakers that crashed on the occasional jumbo frame.