Most likely improper prep work, contamination, no sanding, etc.

Improper cleaning, prep, etc. Residue prevents adhesion. Bathroom and kitchen walls, trim and doors need a thorough scrubbing with Dirtex prior to painting.

Could also be that the paint underneath it is oil based. Latex paint doesn't adhere to oil-based paint. If that's the case, you have to sand the oil-based paint before painting with latex paint.

This happened in my bathroom as well. The previous homeowner painted over alkyd with latex, and no primer.

I had to remove all the latex paint.

It was easy, although time consuming to do. Soak paper towels in straight vinegar, and stick them to the wall.

The acetic acid will finish breaking the bond of the latex to the alkyd, and not really cause any damage to the alkyd paint underneath. The humidity in the bathroom has already started the job for you.

The paint will easily peel off in big sheets.

This assumes the paint underneath is alkyd.

Once all that nasty paint is off, you can prep the walls right.

Wait. Even if it's alkyd paint, the adhesion problem isn't caused by latex over alkyd. The failure is due to lack of proper preparation which is the most probable cause in your bathroom.

Clean and dull. Clean and dull. Clean and dull. :)

Latex over alkyd works just fine if done professionally.

Hi there, @Cgrimes1955-

Without knowing the details, here are a couple of thoughts we can share:

1. Was the surface definitely clean? It is possible that there was a contaminate (this could even be a cleaner that was not completely rinsed) on the surface
2. If the surface was glossy and not sanded or chemically etched there is a potential for adhesion issues as well

We prefer to use a separate primer and then paint rather than a paint/primer combo (sounds like this may be what was used). A dedicated primer will usually offer superior bonding between surfaces.

I hope this helps, and good luck with your project!