Architect IVR fails to parse DTMF on SG1 BYOC trunk

Does anyone know why DTMF detection via RFC 2833 fails intermittently on our Singapore BYOC trunks while US trunks work fine? The Architect flow logs show EVENT_DTMF missing for calls routed through the SG1 edge, yet raw SIP captures confirm the SDP payload contains the correct a=fmtp attributes. Genesys Docs