ok... das war dann doch mal eine andere Antwort die ich so nicht erwartet habe oder eigentlich doch...

We have checked all relevant details of your server.
There is not any issue in switch. No one user of same switch abusing it.
Also we did mtr test and find everything is fine.

Please ensure from your side once, and try different target server to upload and download.

Hope to have inform you sufficient.