Painted top of wall flaking - advice please!

[Cliff J]

Hi all, I was hoping for some advice please. I painted our 6ft high brick garden wall top and side during some good weather in September. I pressure washed the whole wall & top well beforehand. The brick was in good condition and clean. I then used 2 coats of Sandtex masonry paint. It looked great until the 2 recent storms, after which the paint on the top of the wall is flaking quite badly. The paint on the sides still looks lovely. See pics attached.

A friend suggested removing anything loose, then using stabilising solution over the top before repainting again. Any thoughts on the cause / how to remedy it are much appreciated, thanks!