Right, that isn’t surprising since it’s the ambient session that is being created in that line which has no input stream (IIRC) so it prevents PocketsphinxController from being able to start its audio unit.
The loudness thing is less clear. I don’t know the reason for that, but my best guess is that it is related to the route. Playback can either be routed to the external speaker or the ear speaker and one is much louder than the other. Different audio sessions have different default routes and need to be overridden to get different results. PocketsphinxController does re-route to the louder speaker, but it is possible that something about the session mixing is causing it to not successfully do that and then it is only when the new session is created that the sound is fully routed to the speaker. It could also be due to a side effect of the mixing setting, for instance if it does some kind of active volume reduction on the assumption that there are two output streams that have to be combined without clipping.Lastly it could just be a difference between the two different audio session settings that is more noticeable when the session is returned to ambient.