I had the card in use under 20H2 on an Asus Prime Z490 P. After the card frequently lost its connection to the network, I exchanged it for a card from Qnap. I had the same problems with this card. Using the principle shake, knock, kick, I changed the PCI-E slots, i.e. the graphics card to the last slot and the network card to the first slot (near the CPU). Since then I have had no more problems with the connections. I think this would probably have worked with the XG-C100C as well. Because of your request, I updated my system to 21H1 (despite searching, the update was not made available to me). After the installation, my Office told me that there had been a hardware change and that I had to reactivate my Office. I tried this several times without success, despite the de-installation and reinstallation. I then switched my system back to 20H2 and everything works without any problems.

I have this card in use with Windows 10 21H1. The driver is from Marvell dated 30.04.2020, version 2.2.2.0. I cannot observe this behaviour on my PC.
Maybe switch off the virus scanner? I'm not sure if it's the driver or something else that's blocking.