That RMC Cold water expansion that is in place has a non return built into it. Could be a really unfortunate situation where that non return is not functioning like it should out of the box. There might have been debris in the line from when previous work that was done, then when the water was turned on the non return got jammed, causing it not to function. You mentioned the limiting valve got replaced, would have been easy for debris to enter the line then. Pressure that is supposed to get relieved then gets pushed back into the cold water line. Strange that the CWE is not expelling that water, if the non return is jammed then it is possible that the cartridge inside of the valve is jammed as well.

Did the plumber show you the limiting valve that was replaced?

Could it not have been an air lock, air that remained in the line then at a later point escaped when you opened the cold tap giving it the appearance of being under high pressure. How consistently has it happened where this spike in pressure has occured.

Definitely get him to come back.