'Old' issue with the 'new' AF routine

Tank you for your comments.
AstroScience, I think exposure duration is not the problem (number of stars are already saturated with 3sec, I also tested 7 sec without improvement in star detection) but of course I could try 10 sec in the next imaging cession. Other parameters are very close from mine.
Do you have the same star detection behavior in your frames? (I upload a partial AFpack if you want to try)AFPack_85.zip (979.8 KB)
In think it could be the core of the problem, in some dense star field the percentage of erroneous HFR is very important and could cause the observed variation in focusing (as the measured stars change during the AF).
Thanks.
Pascal