Adding students to the groups

Hello everyone!

I'm having lots of problems to add students to the groups. 

For some reason, suddenly some groups will show 52 students for no reason, when only 10 were added. Then when trying to fix that another group out of nowhere will show 150 students. It's such a mess and not easy to fix when this happens. There's no such thing as changing the group for the student, you hace to remove them and then start from scratch.

I'd appreciate any tip or advice!

Thank you!