Fine cracks in new plaster skim coat

[Adkroot]

Plasterers have done a nice job so far, but I noticed several hairline cracks at joint locations at door headers. 1/2” blueboard plaster base over 2x4 framing @16” centers that was framed just over two years ago. The joints that cracked were all at seams on cripple studs that are only 5”long between double header and double top plate, so the framing is robust. House temp is as kept at 58-60 degrees Fahrenheit as per the Plaster’s request, and humidity is around 50-55% prior to application of plaster.
Is this a minor issue I shouldn’t be concerned with or something that I should expect the plasterer to address?
Thank you, Daniel

 

[Wayners]

If boarding around a door I like to fit a sheet over the doorway then cut the doorway out.
Can be done a few different ways depending how you plan it but board joints above doors, especially inline with virtual frame are prone to crack.