Network problem on virtual machines - XENSERVER 6.5 - FO - OVH

Hi, I'm looking for clues - environment - Citrix XenSerwer version 6.5 hypervisor

It has several IP-FAILOVER addresses, several virtual viruses. Everything worked fine for about a year, without reason it stopped.

There is a management network on the hypervisor and no network on the VM.

Together with OVH the equipment was checked - under RESCUE mode the network with FO works OK (interface added - operation tested).

OVH - indicates a configuration problem, which could actually occur if it was the first configuration. However, the first configuration is not.

-> Configurations /etc/systemctl.conf - compared to another XEN in the same version. No problems detected.
-> An attempt was made to transfer FO addresses to another server, deleting and regenerating the MAC to the allocated FOs,
-> The network card was changed on the server to a different one, its MAC address changed, it also did not help (OVH also performed MAC address updates after this operation)