Anyone here still using Snom phones? Incoming call glitch when using Edge Server

I'm noticing a glitch that is happening with our older Snom 710/720/D725 phones, doesn't affect our Audiocodes phones. I believe it is related to STUN / ICE.

When we have an external user that is connecting via our Edge Server (either a remote IP phone or S4B App) and they call an internal extension where the user has a Snom Phone, the audio will drop out after 5-10 seconds. If the internal user with a Snom phone calls that person back, the audio is fine so it is only a one-way issue. Anyone dealt with this issue before?