I have this problem as well. It appears to be an intentional feature after 2-3 minutes of silence to avoid using up minutes. However, this doesn't make sense for Pro customers. There should be the option to disable that feature or to force the mic to resume transcribing if it looks like captions have stopped. It could be particularly problematic for deaf people participating in an audio-only conversation, since they may have no way of knowing whether a conversation is still ongoing and they're missing crucial information.