Is this also from placing and bricking the lintel too soon? Brick absorbes water, it is not to be used without a weather membrane like 15# felt(tar)paper behind it, each seam lapped over the next. And last but not least, there are many non professionals who do masonary work, and make the scenario a big problem. A wet brick or even a dry brick with a poor rate of absorption will influence the height that can be laid.
how many brick courses in a day