Yes, that could well be the problem.
Please keep us informed of any developments.
They replied, with an absolute joke of a response, grrr. I was kinda half expecting this though, here's their response:
Thank you very much for your email requesting information about our product.
Actually it is normal, if we keep using the computer or a phone for long time, there will be caches and the speed will the slow. We need to clear the caches on devices and they will run properly.
And the issue can be resolved by rebooting, we suggest that you can reboot the modem sometimes to keep it running properly. There is no other settings we can change on the modem. So please leave it and enjoy the internet, if you have any other problem, please feel free to let me know.
...oh suuure, cache leaks are entirely normal and indicative of all over computing devices *facepalm*
If my old 15 year old Netgear modem could run 24/7 for a year without needing a reboot or using up its cache, then this one should be able to as well. Does this person not realise that if all caches just filled up and stopped working, then CPU chips would never work!
bah!