Streaming API doesn't start

Hi, we're using the streaming API to interact with an avatar. The avatar is launched at page load, however sometimes the avatar doesn't start streaming at all. The API calls in the network tab are all ok and in the right order and there are no messages in the console to indicate an error.

I've compared the API calls for when it's working to when it's not and they appear to be the same, just the streaming didn't start.