At seemingly random intervals, the LAN ports of my router switch to 100mbps and remain that way until I restart the device. Unplugging and re-plugging the cables does not help. After a restart, everything seems to work fine for a day or two. It's not due to resetting (auto reset is turned off). Three of the four ports have devices that are always on (Hue bridge, Android TV, AV receiver), one port connects to a dumb switch with various PCs.

It doesn't necessarily affect all ports at the same time, but has done sometimes. I can't tell if one port goes first, then others follow, or if it's truly random. It appears to be random based on my observations over the last few months.

The problem happens regardless of operation mode and regardless of WiFi being on or off. The unit does get very hot sometimes, but I haven't noticed a correlation between heat and getting stuck at 100mbps.

The problem only affects the four LAN ports and not the WAN (internet) port, which does always stay at 1gbps.

It's not the cables - all CAT6e and CAT7 - because the problem also occurs with CAT5e and CAT6. It's not the devices - they behave perfectly fine for weeks when using another router.

Once stuck in 100mbps mode, it does not revert back (I waited one full week before restarting).

I think it's a firmware bug where an auto-negotiation happens at some point and doesn't happen again.