Issues with QSW-2104-2T

[MaDc0w]

Hello

Running this configuration I'm having issues with transfer speeds.
When I copy a file from the NAS to a PC, I get full 280ish MB/s however copying the same file to the NAS results in speeds between 40-70 MB/s.
If I plug the CAT8 cable directly into the NAS it works fine in both directions.
Both switches were swapped with other new ones with same results.
Also tried the PC on the 2nd 10GbE port.

Anyone got an idea why this won't work?
Thanks for reading.

[Toxic17]

are jumbo frames / MTU 9000 - enabled on all devices?

have you tried using a CAT6/CAT6A instead of the CAT8 cable?

[MaDc0w]

are jumbo frames / MTU 9000 - enabled on all devices?

They are not. Using default settings of MTU 1500. This works fine when PCs and NAS are on the 1 switch.
Would that be necessary for uplinking QNAP switches?

Edit:
The CAT8 cable is running between 2 floors. It works fine until I use it in the 2nd QNAP switch. It also works with a different switch like a Netgear s3300.