Cracks up wall in corner of room
If the crack is occurring where the new remodeled walls meet the older existing walls, it’s due to shrinkage in the new lumber. 

New lumber has moisture in it that will slowly evaporate causing the stud to shrink. It may shrink only a 1/64” or so, but that’s enough for the new gypsum board to pull away from the existing wall. 

You can fix this by removing the stud (only the stud adjacent to the existing wall needs to be replaced) and install a “dry” stud (a stud rated “KD”...kiln dry) which is very expensive or wait about 1 year until most of the shrinking has occurred. Then patch and paint the crack.