Stream Target -- Akamai behaviour clarification

We push HLS to Akamai MSL3 (and 4) and recently have come across issue of detecting whether the stream is live or not on Akamai.

We detect the presence of the playlist.m3u8 on akamai and when it returns 404 (after the encoder stops) we know the stream has ended. Until recently. Now the playlist.m3u8 remains for days after the encode session has finished. I have taken on the mammouth process of trying to talk to Akamai support to get this figured out.

I would like to know, from Wowza support/experts, whether the top level manifest are sent periodically to the stream target OR just once at the beginning of the stream session. The child manifests (chunklists) are obviously refreshed at the similar frequency to the chunk duration but how often do the top level manifest get posted?

If I were to were to add a new stream (new bitrate) to an encoder group, this would force a new manifest to be uploaded, so there is a mechanism to send interim top level manifests… How oftern is this invoked in the normal case.

Thanks,