bubbly/cracked paint
There are a few reasons that paint wrinkles. The most common reason is using an oil based primer or paint over a latex painted surface. If you only have a small area of problem, this is probably not the case. I suspect you may have left some wallpaper sizing or glue behind. Some soap may have leached behind the wallpaper also. When removing wallpaper, it is very important to really clean the surface well. Sometimes a skim coat of joint compound is needed to smooth the walls and create a good bondable surface. Another possible cause is that the primer was not dry enough when you painted. If the primer didn't wrinkle after it had been on and cured, then maybe something contaminated the surface before you painted.  As you see, there are several reasons for the paint failure.  Check the options or add more detail to the question.