Webrtc softphone fallback to sip on byoc trunks in ap-se-2

quick question about webrtc softphone behavior. when the agent’s browser drops the webrtc connection, does it automatically fall back to sip over our 15 byoc trunks in ap-se-2? we see 408 timeouts during this transition. the architect flow shows successful routing, but the client-side logs indicate a handshake failure with the carrier. is this a known quirk with specific carriers in singapore?