You receive this warning message in a call when no calling relay (TURN server) is reachable and you may not be connected to all or some of the participants in your call.
This can happen when Wire is behind a firewall or proxy.
If a participant in a call can not be reached on a direct path the calling relay is essential to connect the call successfully. Especially in a group call this may lead to unexpected behavior, for example the call may get connected to participants that are on the same local network but not to participants that are on a remote network (for example missing participant(s) in the call).
To avoid calling issues, please make sure your firewall and proxy settings allow connectivity to Wire calling relays.