GS110MX Incredibly Slow (5-10mbit/s) in one direction

Hello everyone!

First off, i don't have the EMX Model, just the MX, so unmanaged, but i couldn't select it in the "Model" dropdown for some reason.

So here goes nothing:

I recently bought a used GS110-MX, which has two 10G (and 2,5G/5G!) ports, however, one of them can only receive and not send.

Here's an iperf, once from PC to NAS, once from NAS to PC.

I tried this with multiple PC's and the switch is always the one common factor. I tried with my other two 10G switches and it's fine.

It's worth mentioning that it's literally only 9mbit, Accessing the NAS through this just doesn't work, it's incredibly slow.

The Switch itself DOES however indicate the port as being 10G with both Green Lights blinking. 

Interestingly it seems to be just Port 9 not working, because when i switch NAS and PC ports on the switch sending gets fast but receiving will be slow. 

One more thing, the 9mbit is actually fast, usually it'll sit at around 5mbit, so it's not accidentally in a 10mbit mode, which the port doesn't even have iirc.

When i give it more clients it also WILL go faster, but not really by a lot.

The previous owner told me in his possession the switch worked fine, but he can say all he wants at this point....

Any ideas?

Thanks a lot!

EDIT: For some reason it doesn't show my pictures...

EDIT 2: Here's a thread by gmctavish who had a similar problem but unfortunately didn't follow up and hasn't been seen since.
https://community.netgear.com/t5/Smart-Plus-and-Smart-Pro-Managed/GS110EMX-10G-Port-get-REALLY-Slow-Odd-but-repeatable-solution/m-p/1881515#M15094