Logs confirm that everyone got connected to the same channel (logs coming from VivoxCore), however the participants list is never updated (having only the local user on it) and you can’t hear other participants.
Searching further, seems like Vivox is only officially supported up to Unreal Engine 4.26, is that still true?
Is there a known workaround to get it working on Unreal Engine 5.1?
EDIT: worth mentioning that it works fine in both Echo and NonPositional channels, only having issue with Positional channel