When drawing model 1 is referenced into drawing model 2, it shifts despite callouts being in the same plane.
The issue has been solved by deleting all of the folders in this directory C:\Users\bp\AppData\Local\Bentley\AECOsimBuildingDesigner\8.11
There were two folders in the directory which contained both SS3 and SS4 AECOsim applications – 2 sets of preferences. When both were deleted, the problem was solved.