It is not much clear from the photo weather there is failure in surface of bricks for bonding or the lack of curing along with higher thickness of plaster.
When the thickness of plaster is increased, Mason normally do have tendency to do plaster in a single layer for full thickness by dry shaking of cement on wall surface. when thickness is increased there is a chance of settlement and de-bonding of plaster from wall surface. not curing the plaster makes it further more worse by de-bonding it on larger area.
De-bonding can also be accounted for not doing pre-wetting of wall surface specifically on walls next to street where lot of dust is emitted and settled on wall surface from long time, if not cleaned by washing wall surface (pre-wetting), this can cause a de-bonding issue.
You need to do further more close inspection to identify the root cause of the same.