Dedicated Server in vRack with /28 IP Block - main interface/IP not responding anymore

I'm having a dedicated server with a main IP address (eno1)
everything is working fine.
I ordered an IP Block and wanted to have the server in a vRack together with the IP Block

I configured my server as followed:
* eno1 remains on the main IP (1GBPS link)
* eno2 is assigned to a bridge (br0) <-> br0 is having the 1st usable IP from the block (100MBPS link)

after a reboot, the server is not anymore answering on the main IP
only the 2nd IP allows access to the server

as the monitoring of the server done by OVH is related to the main IP, the server is always going into rescue mode, support is raised ... which makes my server not usable anymore

from the server, I can ping the main IP (hopefully) and access internet (using the IP Block gateway)

Any idea why the main interface is not anymore responding in my case ?

Thanks
Sylvain