@Kevin_Z Resetting the router to stock settings appears to have fixed the issue for now, I will do all of this and report back if the issue returns.

Hey there, I'm having the same issue with the same router and firmware version 1.2.5 Build 20190411 rel.52981(5553). I had the same issue on firmware 1.2.2 also. We should be getting around 200 Mbps...