I'm having a hard time with the failover server. Was never able to get it to work properly. I don't think the way it's currently done, is intuitive, and even harder to provision and program. DNSSrv is even more annoying to setup because not all the manufacturers support it, or even implement it properly.
Using Yealink and Grandstream, it's extremely simple and straight forward. Simply put the backup IP and if the main server goes offline, then it automatically failovers to the backup server.
Do you plan on implementing this type of setup? It is currently the only feature swaying us away from Snom sets.
Which phone and what version of frmware? Are you using the method outlined here https://helpdesk.snom.com/solution/articles/6000136224-failover-identity-does-not-revert-back-to-primary-identity-after-re-established-connection
Currently, I'm updating the phones to 184.108.40.206. This includes all the Snom 3xx and 7xx. I think the failover idea that is currently implemented is very poor compared to the rest of the other brands out there.