EE broadband constantly high latency on ethernet connection

[Bo-oF]

The upload latency is constantly over 200, hovering around 220 - 280ms. This makes gaming literally impossible. Openreach have checked the line and have found no faults, EE technitian also found no faults within the service. We recieved a new router but the problem still persists. I have tried using all different ethernet cables (all Cat5e) for each connection. The service was working fine until about 4 weeks ago. EE have stated that there is nothing more they can do and offered a free cancellation. I have never experienced this sort of problem with any other provider. I have tried the network under loaded and unloaded situations and the results are the same, as well as only 1  device on the network (ethernet connected pc). The computer is mid end (3600x, 5700xt) so there are no issues with hardware. The issue still happens over WiFi on all my devices. The speeds are exactly as advertised (100D 20U), as well as the download ping being normal (for uk servers 16ms - 20ms).

[Bo-oF]

Just want to reply to say your theory about buffer bloat is absolutely true. The results have remained the same, as well as my entire network and devices, but I recently upgraded to Gigabit through EE. I have the same router and devices connected but now when I do an ookla test I get ping as expected, 18 - 24ms, on both download and upload latency.  I myself am looking into new router, since the EE router has had nothing but issues, appalling range, instability with VR streaming (in the same room as the router) and this entire latency issue.