White because the screen stretch your processing software used is not within the normal range that VPhot expects. I tried to fix it under tools>display without success.
You might try saving it as a 16 bit, not 32 bit, image in AIJ and upload again?
Yes, yes, thank you! Indeed after saving in 16 bit all stars disappeared.
But camera gives 16 bit gray image, and 32 I got after stacking. Well, I'll try to correct my clumsy processing, now the reason is known.
16 bit helped, but all bright stars have white circle in the center - I think, it shows on oversaturation?
Probably, better to try single shot or other type of stacking. Maybe better to stack 30 10-sec frames in VPhot, but what to do with flats and darks?