losing main stars in SiriL registration

[kinetic]

Hi all,


I'm a recent convert to the program SiriL for registration and stacking.
Can anyone please tell me why I occasionally lose main stars in a registration and stack?


Not always, only sometimes.


This set I lost Mimosa in the Southern Cross.


Data on other nights stacked fine.


It's quite puzzling.
I have tried 1 star registration and multi star registration.


Thanks for any tips in advance,


Steve