Okay, I've got a weird one, that both me and my Internet tech (and his boss) confused. 

I upgraded from 1Gbps to 2Gbps.

If you plug a device directly into the modem, it's getting 2Gbps Up and Down.

When I plug my Deco BE23 router into it, I'm getting 1Gbps download and 2Gbps upload.

I've tried replacing the Ethernet cable in case there was something funky with it, and I've made sure the firmware is up to date. 

Any ideas what could cause something like this??