The facts appear to be:
1) This wall gets some severe weather, and over the years, the brickwork has
been badly affected, probably by rain / frost cycles.
2) Some braindead clown has painted the walls in the past, in an effort to
hide some of the badly affected parts, instead of cutting them out and
replacing some of the bricks as was required.
3) You are now lumbered with a damaged wall which is getting steadilly worse
and will continue to do so until it is completely overhauled, because the
paint traps moisture in the brickwork.

You now have several choices:
1) Patch up and repaint - 'make do and mend', which is only a temporary
measure, which is what has already occured, maybe several times
2) Completely overhaul the entire wall, which means complete removal of all
of the paint by fair means or foul, IE sandblast the whole thing, then cut
out and replace any damaged bricks, and finally repoint the whole thing.




Option 1 can be more than temporary if you use a solvent based masonry
paint such as Johnstone's Storm Guard. I hate painted bricks as much as
anyone but option 2 may not be feasible for most people.
Paint doesn't hold water behind it if it's well bonded to the substrate
and produces a rain proof seal. The problem is that water based masonry
paint don't do this.