its all in the prep work.
hmmm, long ago, 25 to 30 years there was no such thing as primer, primer was actually flat paint. So, the flat was a sort of primer and a finish coat.
was the primer latex, and was your finish coat oil? Or even vise versa. Sometimes with cheaper paint the two will not stick to each other.
Was your paint put on too thick?
Did you put on this paint over a damp or moist surface?
Did you use the shower area and create steam before the paint had a day or more to dry?
Did you stirr up the paint by hand for 10 minutes stirring from the bottom up? If you had it professionally shook never mind this.
Did you put on multiple coats without the preceding coat to dry?
As you see, there are many things that could have happened.