I detach the difficulty banner from minimap and move it to the most bottom-right corner, Vertical = -540, Horizontal = 960.

For a period of time, maybe from the launch of BfA till today, I have observed that the difficulty banner would move out the corner and appear at a top-right position, near Vertical = 500, Horizontal = 810, which looks like the default position for the banner.

This only happens when I'm in non-guild mythic+ teams. It seems every other difficulty banner is fine.