Speed issues using TP-Link Router behind Pace 5268AC
I'm at my wit's end. (Hopefully I'm posting this in the correct spot.)
I use a TP-Link Archer C2300 router plugged in via ethernet cable into the Pace 5268AC Residential Gateway (ATT Uverse).
I'm on the 100/20 internet package and if I plug my laptop directly into the 5268AC via ethernet, I consistently get speeds of 95/20 if not better, every single time.
But when I use the TP-Link app that tests the speed directly into the C2300 router, using the same kind of ethernet cable into the port right next to the one my laptop tested, it gets anywhere from 30/18 to 75/20, averaging around 50/20.
This didn't start happening until about a week ago. Up until then, the C2300 was testing at the same speed as the laptop plugged directly into the 5268AC.
What gives? Did something change via firmware in the past week?
Thank you for any help!