Hello,
I tried to solve the problem through support, unfortunately without success. Maybe there is a Lightburn programmer in the room who will be more interested in the problem. It is a bug - a confirmed bug.
When we apply a mask that consists of an outer and inner element, then we group such an element with the mask, then we save the project. It is after opening the project that the mask disappears - the element that had the mask when saving after opening the project does not have it. The problem occurs only when the mask is composed of an outer and inner element (all explained in request #163092). The problem has been known for over 2 weeks and during this time 2 fixes were issued. Unfortunately, none of them fixed this issue.
Best,
Alex