How to repair latex paint on drywall in bathroom?
This is surely moisture related.

So first, check that the fan is properly vented! Sometimes a vent fan simply dumps into attic space above the bathroom.

Second, run the fan for a longer time. Timer controls are easily installed, in place of the switch. It can be set to run for up to an hour, making sure the moist air is properly exhausted. With a timer, you can set it, then walk away, knowing it will shut off after the set period of time.

As far as repairs to the existing walls go, you MUST first stop the moisture, or it will simply happen again.

Once that is done, only then should you fix the walls, the ceiling, the paint. If there is bubbled paint, it must be scraped down, down to a solid surface. If the wallboard beneath it has bubbled, then you may need to replace parts of it. Cement board is a good idea in a wet environment anyway.

If there is any mildew, it must be killed. Chlorine is one way, but if it has gotten a foothold in the wallboard, then pull down that wallboard.

Once you have a solid substrate to now re-finish, paint, wallpaper, and tile are all viable ideas.

One solution can be to use wallpaper. It will help hide some flaws perhaps more simply than paint, but if this is just done to hide a problem without first stopping the problem, then it will peel off quickly.

Where paint will be used, always use paint that has had a mildew-cide added to stop the growth of mildew. If the wallboard itself has bubbled, before you paint, make sure any holes have been smoothly patched first or they will show through the paint. If there are any stains, Kilz (or similar products) can help to seal those stains before you re-paint.

Tile (my personal favorite) can be more resistant to water than wallpaper or paint. So you may choose to extend the areas that tile covers.