A project I've been providing technical support to has RTL marks sprinkled throughout where they don't belong. The project is a back translation of a RTL project, but all of the text is in English.
I don't know how they got there, but I did notice that the RTL marks are mostly in or near verse numbers:
\v 2[RTL mark] Text of verse 2
From what I understand, in a RTL project, when a verse range is specified (e.g. 1-2), a RTL mark is placed before the hyphen to cause the verse range to be rendered correctly. Since this project is based on a RTL project, perhaps the USFM structure, and hence the RTL mark, was copied into the daughter project? That doesn't explain why the RTL mark would be present when there is not a range, but perhaps the versification was changed at some point.
Can Paratext be made to show invisible control characters? As far as I could tell, the basic checks were not catching the RTL mark.