This request is one more dupe - to a very long standing issue.
Unfortunately, “Auto Mask” generally does not work in a reasonable way at all. 
Also see Shortcut to observe the actual auto-mask?
(and particularly the links I provided in that thread).
In fact, it is really frustating that this issue apparently is completely ignored by DxO for several (more than four) years now, despite of a fix being promised for almost the same time…