My Ethernet throughout the house is done with Cat5e wiring.

 

My router is the latest 3BB WI-FI 6 router, and LAN cable to my office is plugged in directly to the router

 

My device has Gigabit Ethernet adapter, though I get only 10/100 network in the office

 

If I take the device to the router and plug it in there, I get Gigabit download, so router and device are working properly.

 

Cat5e supports Gigabit speeds, so what can be wrong that I only get 10/100 network in the office?

How long is the cable?

Cheap cat5e cables might not actually meet the specification, and if they are a bit longer you won't get gigabit.

Solution: Get a better cable.

How long is the cable?

 

Have you verified that all the cores are correctly connected?

 

In the meantime it is sorted.

 

I enabled Root and Magisk on the box, after which it rebooted, and then got Gigabit network and speed in the office.

 

To double check, I then removed Root and Magisk, box rebooted again, and I still had the Gigabit network.

 

Not sure why this happened, as I obviously had rebooted the box a few times previously when moving between my office and the room where the router is.

 

Thanks for the replies