Bandwidth Speed issue via Router but fine direct with Modem

[Nonleague]

Router: XR300

Firmware: 1.0.3.50_10.3.36

IPv6: Disabled

QoS: Never

QoS settings: Down: 75.06mb UP:18.86mb 75%/75%

Connection: PPPoE (entered in Router as cannot enter it in Modem)
 

So I have been using this router for about 3-4 months now with no issues, however the past 5 days I noticed that my bandwidth speed had reduced from 75mb down to between 35-50mb and the upload had maintained it's 18.5mb upload. I called my isp 3 days ago as I thought that perhaps it the issue was with them but they informed me that everything was fine at their end. Anyway I play FIFA 20 on the PS4 and had been using the QoS set at 75% up/down  with no issues until 5 days ago. When I switch from 'High Priority Detected' to 'Never', my download speed will increase from around 40mb to 50mb regardless as to whether the PS4 is on or not. Now this should jump to 74 or 75mb like it always did before.  If I completely disable the QoS then the speed increases to around 60-62mb down.

To eliminate the Router being the problem I connected the PC directly in to the Modem and straight away the speed jumped to 74mb down which is what it should be.  I have done several tests like this and it is stable between 72-74mb down when connected directly and bypassing the Router.  So the issue is the Router.  All cabling is recently new and is the exact same cable used so cabling isn't an issue.

I followed the guide below and this has not solved my issue.
http://support.netduma.com/support/solutions/articles/16000076586-dumaos-optimal-settings-guide-maximum-bandwidth-speeds

 

So my question is, what can I do to fix the problem or does the router need to be returned?

 

[Netduma Fraser]

Hey, welcome to the forum!

By completely disabled do you mean toggling the disable option in the Anti-Bufferbloat 3 line option menu? Did you change any settings or anything to do with the setup when you first noticed the issue happening? What speeds do you get via WiFi? Where are you testing the speeds?

[Nonleague]

1 hour ago, Netduma Fraser said:

Hey, welcome to the forum!

By completely disabled do you mean toggling the disable option in the Anti-Bufferbloat 3 line option menu? Did you change any settings or anything to do with the setup when you first noticed the issue happening? What speeds do you get via WiFi? Where are you testing the speeds?

Hi thank you for your reply.

1) Disabling it by clicking Anti Bluffer bloat and then unticking Disable QoS not recommended option. I also select for it to be on NEVER.

2) I didn't change any of the settings on the router, it just started happening as described a few days ago.

3) I have been testing it extensively using speedtest.net and also speedtest.btwholesale.com/details

4) On wifi i'm getting 72mb down and on LAN with QoS disabled I'm getting 62mb Down.

[Netduma Fraser]

The WiFi speeds would indicate a specific wired issue, do you get this on ALL wired devices? 

[Nonleague]

22 minutes ago, Netduma Fraser said:

The WiFi speeds would indicate a specific wired issue, do you get this on ALL wired devices? 

You would think that except I get max speed when using the same wire plugged directly in to the Modem, thus bypassing the Router.

[Netduma Fraser]

I get lower on that speedtest as well, try fast.com and in fast.com settings change parallel connections to max 20 and test duration to max 60 and see what you get.