I have the same IP address for cloud.mydomain.com and office.mydomain.com
But i have 2 differents frontend and 2 differents certificates for each one.
Certs were delivred by Let’s Encrypt ;).
To be sure that the problem is coming from HAProxy config or something like that, i will get an additional IP address, and i will NAT this one directly to my Collabora server.
I will report my experience soon.
Thanks for your help again 