If you have a spare router put that between the modem and XR500 to handle PPPoE and let us know if that resolves it please.
Thanks Fraser, but i think Zennon's post hit the nail.... I remember the same thing happening with my previous Nighthawk R7000 , PPPoE overheads makes sense... .
I must look into setting my unlocked Openreach HG612 modem to use PPPoE, together with the XR500.
I'm just afraid to start as it may bugger-up all my current settings for CCTV, remote access, Teamviewer, Filtering on DNS etc etc. it all more or less works at present and don't want to mess it up.
if anyone here has done this setup already, please post details on the HG612 modem settings, and the XR500 settings. Would save me a load of experimentation time.....