It is hit or miss with the new bobbins when it comes to my vintage/antique Singer sewing machines. I am having most of the same problems as you. Sometimes the class 15s will only go onto the bobbin winder on one side but not the other. Some do not have the little notch on the center edge and will not go onto the bobbin winder properly. It doesn't matter if it's Singer brand or off brand.
My antique Singer 66 does not like new plastic Singer brand bobbins at all. They cause all kinds of tension problems. i haven't tried new metal ones.
Off topic: As a fellow migrainer, I find it fascinating that Butters can alert you when you are going to have a migraine. Taking medication at the correct time can makes such a difference for me.