Yes in deed, I also thought that this is the behaviour. But forcing a sync does not help. And the GetEpisodeDetails call is done everytime I start the episode in okay.log. While generating this log I did not force a sync.
The call is throttled when you browse an episode to update every time you look but as said it’s unrelated to streaming.
If you swipe down that call is made and Yatse is updated. If Yatse still don’t have duration then Kodi does not send it. You have all in the logs to see.
I still did not make any progress on this topic. I already deleted the host in Yatse an created it new. This also did not help. GetEpisodeDetails is never called. If I reload the episode details with the swipe GetDirectory is called, although I triggered it via the shows menu, not via the files menu.
You are mixing things again 
GetDirectory is called when streaming to get the subtitles.
GetEpisodeDetails is called when you swipe down on an episode or browse it after a delay long enough to trigger a refresh.
to full sync GetEpisodes is called but should return the same data as GetEpisodeDetails.
I finally made it. Yatse takes the duration not from episode.c09 but from streamdetails.iDuration. After inserting the value also in this table, everything is working fine. Thanks for the support.
Yatse does not choose and take what Kodi send 
And yes I talked to you about the stream info as soon as you talked about c09
But Kodi should return c09 if there’s no streamdetails. Anyway this is Kodi internals and Kodi is often bugged and do strange things 
Glad you find out, but you may want to ask Kodi Team to add an API so that remote can trigger the stream scan since it’s no more automatic