You seem annoyed. Thats not going to help. I don't get easily flustered. And I'll still try & help. (By the way I always read the complete post).
So what remains to test:
1. As per my suggestion above - try using both NICs for vmbr0 vmbr1.
2. Try changing Processors
: type
in VM. Maybe start by trying host
(last one in list).
3. Try changing Machine
: in VM. Maybe start by trying Default (i440fx)
4. Have you tried a bare-metal install with a different OS on this same machine - with no errors. (CPU, RAM, USB, NIC etc).
5. We are assuming your network infrastructure & topology are not the cause. But maybe you need to look at that more closely.
I get the impression - you don't really want / trust my input. So I would rather not impose.
If that changes - just shout out - and I'll gladly try and help again.