I have an old Supermicro server, based on the X8DTL-iF motherboard, and Microsoft Hyper-V Server Core 2019 installed.
The server motherboard has 2x Intel 82574L Gigabit Ethernet Controllers.

When server starts, network works as expected. But after some time server goes unreachable. The host and most of VMs cannot be reached. After connecting to the Hyper-V console via virtual console (server has dedicated IPMI NIC, and it works without flaws) Windows Server shows no NICs. After reboot it works again… until next time. Note that I have access to the VM 1 even I can’t reach host (Hyper-V console).

Server has firmware and BIOS updated to their latest versions. Hyper-V server is enough fresh too.

How can be this error solved?

There is a LAN adapter for server itself, and LAN adapter for VM 1 and VM 2 (LAN2) with external access, and virtual switch (InterVM) for VM 2 and VM 3 without external access.

I have excluded host access for second network adapter but I still have no access to the host and some VMs.