I'm not with Voxalot and don't actually use it on a daily basis. I find SIP and network issues to be like puzzles, they can be interesting to solve.
Regarding the issue with your Snom, Voxalot calls seem to be incoming normally for the rest of us. The SIP error messages indicated your phone settings may be incorrect, which wouldn't necessarily prevent it from working elsewhere.
It seems Voxalot support personnel are a bit scarce. I have seen a number of people come with urgent issues, but no help was offered by actual tech support people. For example, while trying to help this person
HERE, I identified a problem with Voxalot's (claimed) ability to operate on non-standard ports. When no one from Voxalot tech dept responded, I even made a separate thread,
HERE, and yet the problem remains.