MWI on 1.6.2 not working - no notify

I’m been trying to troubleshoot getting MWI to work effectively in my setup with no luck so far. The setup is as follows:

FreePBX 2.7 (latest version)
snom 320
public IP for PBX without NAT
snom 320 behind nat

  1. BLF works without issue and notifies on ringing/busy for monitored extensions work with no problem
  2. MWI does not work. No MWI until about 30 minutes after voicemail is left.
  3. No notify event in sip debug for MWI for peer

I know MWI changed significantly in 1.6.2 but why no notify? Anyone have suggestions on things to check?

I opened an issue on since there doesn’t appear to be any workaround. Issue #0017398.