Maybe it's related  to the CentOS 5.2  e1000 kernel module .
Can you install  another CentOS 5.2 and verify that the issue exists?
Any chance to upgrade the VM to 5.11 or just update the kernel so it is at least  2.6.25 , so you can try the virtio NIC ?

Best Regards,
Strahil Nikolov

On Jan 12, 2020 20:03, Latchezar Filtchev <Latcho@aubg.bg> wrote:

Dear Strahil,

 

Last strange discovery. Newly installed VM – same OS, same NIC’s – connected to the same VLAN’s. Both machines are running on the same virtualization host.

Newly installed VM – no network issues at all. It works flawlessly.

 

It is really very strange.

 

Best,

Latcho