R8000 Nighthawk X6 AC3200 only gets half internet speed

Hello guys,

So here i come with my weird issue. My router simply drops half bandwith (download only) after 24 hours. Let me explain. My ips bumped my bandwith to 200mbps/30mbps from 100/20. After running several speed tests, i only got 100 / 30. Reseted modem and router, finnally got 200/30 but the next day back at 100/30... Even with modem/router reset couldn't get the bandwith back to normal. So i decided to roll back firmware version to initial and see what i get. Take a look at those shots taken yesterday evening after the firmware rollback:

Thought i fixed my issue ! But this evening... after coming back from work...

No matter on many time i run the speed test, same thing... Even through speedtest.net. Can't get my bandwith back. If i reset the modem and connect directly to it tho, i get full bandwith !

Let me give you some details on my router settings:

Firmware: 1.0.0.46 (upgrading it back in a moment tho as the problem remains)

Turned off WMM: Forgot to specify - This fixed the issue the first time a week ago !

MTU = 1500 (tried 1300 - 1400 - 1450 unsuccessully)

Internet port statistics:

Anyone having an idea?

Thank you very much guys !