No longer receiving transcription callbacks from conversationTranslator using microsoft-cognitiveservices-speech-sdk

Question

We've been using Multi-device conversations with the microsoft-cognitiveservices-speech-sdk in our video conferencing software for some time now to provide real time voice transcriptions. We have a C# backend which does all the conversation management and adds participants to it. The front end is then written in javascript with each client using a conversationTranslator instance to connect to the conversation, stream audio to microsoft and receive text transcriptions in multiple languages. This has been working mostly fine up until this point, with the occasional disconnection issues.

Recently the callbacks containing the transcriptions have just completely stopped working, and the clients aren't getting anything back when they speak. Upon joining the conversation and calling startTranscribingAsync() we get a successful response, but then the conversationTranslator.transcribing and .transcribed events aren't firing at all. I've updated to the latest version of the sdk (1.20 from 1.18), and no other relevant code has changed on our end. I can't see anything of relevance in the release notes since 1.18, anyone got any idea what could be going wrong?

Thanks