I've some troubles with Siril. I photographed the Embryo neblula (NGC 1333) without guiding, so my sub exposures are only 15s long. If I try to register the images, Siril only registers half of the images. I don't understand, why Siril can't align the stars in the images:

Why is this image registered but

this image isn't?
The console only says "Cannot align the stars".
I use the 2 or 3 star alignment method, because every other method worked even worse. I use the bright star in the middle of the image and the bright star in the upper right corner.
Kind regards,
Sternwarte Orion