In Camera Raw 22.214.171.1248 in the Heal panel after the first click to heal, dragging with the right mouse button down no longer changes the brush size. The horizontal double arrow cursor is still displayed, but dragging left or right has no effect.
Moving the size slider, or simply clicking in the numeric field to the right of the size slider, restores normal operation. However, after the next click to heal, right-dragging stops working again.
In Camera Raw Preferences > Performance, I selected Use Graphics Processor: Off, but this didn't help.
This issue should be fixed in the Camera Raw 13.2 update that went live today. This update includes fixes to some of the top customer reported issues among other bug fixes. See: Fixed issues in Camera Raw