Audio cuts for a few seconds when calling from Teams to a non-Teams number

Hello team,

We're experiencing an issue for the following call scenario :

Internal Teams user calls a non Teams user (routed to PSTN via SBC)

For this call scenario, the non Teams user hears audio at the call establishment (about 2sec), then he experiences a few seconds (2,3sec) with no audio, then audio comes back again during the call. The internal Teams user doesn't have this audio issue during the call.

The design is per Asia model (Proxy and Downstream SBC) and media bypass is enabled on MSFT. Version of both SBC clusters is 840p8.

At first we thought we were hitting