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 From: Strahil <hunter86_bg(a)yahoo.com&gt; Sent: Sunday, January 12, 2020 5:58 PM To: Latchezar Filtchev <Latcho(a)aubg.bg>; users <users(a)ovirt.org&gt; Subject: RE: [ovirt-users] Re: Unstable VM network connectivity after upgrade 4.2.8 to 4.3.7 I guess I didn't clarify myself. I asked if you can shutdown the VM and then set only this VM's 'Custom compatibility mode' to 4.2 and power up to test. Yet, if the cluster was at 4.2 when you imported , then I am afraid that the 'Custom Compatibility mode' won't make a difference. I'd recommend you to open a bug on bugzilla.redhat.com<http://bugzilla.redhat.com> and share the link with the mailing list. Many of the dev take a look here. But st Regards, Strahil Nikolov On Jan 12, 2020 15:02, Latchezar Filtchev <Latcho@aubg.bg<mailto:Latcho@aubg.bg>> wrote: Yes! It is. After upgrade 4.2 to 4.3 datacenter and cluster compatibility mode was 4.2 when I discovered the issue. Then I set Cluster mode to 4.3 – no luck. It is not so easy to return it to 4.2. Thank you! Best, Latcho From: