This was not the case in 4.20. But the issue appeared in 4.27 when i was trying the convert my project from 4.20 to 4.27. In my game you tag object using a binocular. The binocular effect uses camera fov scaling. The camera is not moved.
In 4.20 when i zoom in/out on the material billboard object, the size will change, keeping the screen size constant.
The is an unresolved UE entry regarding this. link - Unreal Engine Issues and Bug Tracker (UE-97763)