Didn’t realize…did you file a ticket with support when it happened so they could add it to the list? 
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Probably the winding order issue. That one is usually fixed by opening in Inkscape and resaving. I don’t like having to do that though 
And there are some folks who aren’t able to navigate Inkscape easily so it doesn’t necessarily help them.
The reverse path command in Corel doesn’t seem to change the winding order so that doesn’t help either. I keep looking for the solution.
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If you reverse a closed path it must change it’s winding order. The direction of the path (clockwise / anticlockwise) is its winding order.
The kicker, I think is not to reverse them all (which somebody said they did) because I don’t think that helps. You want to have them alternating for completely nested paths to have the winding rule give the same result in both cases. IIRC. I admit, I didn’t think it through carefully. 
You need islands in one direction and holes in the other, regardless of nesting.
Yeah, that makes sense. And then the thing to watch out for if you’re working around software that applies the same rule to everything regardless is paths that cross themselves. Simple crossings work, but more complicated examples it doesn’t matter which direction the path goes, the two rules give different results.
I think if you use fillrule:evenodd and make all islands one way and holes the other (I can’t remember which is which) then it works even when things overlap. For example two overlapping holes make a hole that is the union of the two. Same with overlapping islands.
When you use the default fillrule:nonzero you get the symmetric difference when you overlap shapes. That isn’t useful when cutting out physical objects. It does give nice 2D patterns when printing.
I was once got roped into demonstrating 3D printing at a Mini Makerfair in Manchester. The guy organising the stand gave me some STL files to print. His came out correct but mine had big holes in them. The reason was he had overlapping meshes in his STL that should have been unioned and he used a slicer that applied fillrule:evenodd to the 2D slices and I use one that uses nonzero.
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For Corel I had a design I was helping someone with. A half-dozen objects one of which wouldn’t translate correctly as an island in the GFUI.
If I opened the SVG in Inkscape and saved it, it worked.
I checked the SVG file from Corel and found the winding order problem and it was not in the SVG saved from the Inkscape file.
I did a reverse path operation in Corel, verified from the indicators on the path that it now matched the other objects. Saved it as an SVG and it still had the problem.
So I know it shouldn’t but it does. It just only happens maybe 1% of the time so I don’t sweat it. I can see when it happens by looking at the thumbnail in the GFUI so I don’t even waste any materials.
The path direction difference was caused by the object being a mirror of another object. But that doesn’t always result in the issue in the SVG because I routinely mirror & flip objects to simplify things like my flat pack reindeer.
Thanks everyone for all of the help. Since you were able to find a fix, I’m going to close this thread - if the problem reoccurs, go ahead and post a new topic.