An exterior porch with closed over head roof. Whatever caused it to
loose bond will likely happen again unless you find out what is causing
it and fix. Most likely it is under vented allowing moisture buildup to
push out on the paint. There should be bottom and top roof vents, or add
more if there already, this assuming no leaks. Whatever bad paint you
left on will likely peel , removing everything loose or even all the
paint since it is suspect. A typical job would be T&G plank as it allows
some air to pass. You may always have problems with drywall but getting
off old paint will help.