Just to add some additional testing I did late last night. I tried my AC1900 router again, after factory resetting it. Connected it to the SB8200 modem and rebooted the modem. This time, I had ~900Mbps download speeds going through the AC1900 router, with my wired laptop!
I then tried to switch it over to my AC3100 router, without rebooting the modem, but my router had a WAN error that said "Your ISP's DHCP does not function properly". So, I rebooted the modem and the AC3100 router, and let it all come back up and online. I then had ~900Mbps download through my AC3100 router. At that point it was after midnight and I went to bed, hoping for the best.
However, I got up this morning and everything was back to ~30Mbps download 😞 Several modem reboots already and no change, ~30Mbps download.
Hmm, if the speed is coming and going, I doubt it's the config file. Could you post your signal levels? Also, anything critical in the logs? Maybe a failed firmware upgrade? Partial service error?
