Internet drops at bandwidth saturation

[pleb]

Hello,

since about one week whenever i'm saturating my bandwidth (mostly downstream) and it goes above 50 Mbps, i start losing connection. It gets worse when im at full speed which is 300 Mbps down. My pfSense is running as a VM on Proxmox 6.1.

Hardware is a ZBOX CI327

CPU: Intel Celeron N3450 (4x 1.1GHz, up to 2.2GHz)
Disk: Samsung SSD 860 Evo
NIC: 2x Realtek RTL8111/8168/8411

I am aware that RTL is a trash Adapter, but i never had these problems before. I called my ISP and they claim that everything is fine on their end. I only had a Netgear WNDRMAC (N600) to test it with, while it max outs at ~250 Mbps, it is stable. No timeouts whatsoever. When i download files on the Proxmox host it doesn't timeout that "easily". Nothing useful in the logs.

Disable Gateway Monitoring Action is checked.
Stage Killing on Gateway Failure is unchecked.

Does anyone know where i can start troubleshooting?

[marvosa]

A device with a Celeron CPU and 8 GB of ram wouldn't be my first choice to install a hypervisor on. Not to mention, the Realtek NIC's aren't doing you any favors either. The first thing I would do is install PFsense on bare metal and blow Proxmox away. Also, if that ZBOX is modular, grab some Intel NICs.