Hi Alex, it's probably some areas of self intersection. Any flipped direction curves should be automatically reoriented but self intersections will cause that kind of thing.

The way I'd narrow it down is to use Construct > Planar starting with just the outline and one interior letter and then if that's ok use undo and add in another letter until it gets messy then you can inspect that particular letter more closely. A good way to inspect it is to turn on control points and then yank each one over and if it shows an expected connection that will be the problem area.

I found the first one on the "t" here:





- Michael