A que se debe que la letra se distociona al pasarlo de vector a otf

No se puede decir eso exactamente. Sospecho que los objetos de la trayectoria tienen demasiados puntos o tangentes demasiado largas.
Puedes optimizar los objetos de la trayectoria en AI y luego volver a intentarlo.

Hi, there is a new bug in Illustrator since versions 25.3 which may result in such an issue. 2 temporary solutions until Adobe fixes it:

  1. It should work fine if you load Fontself from an older version of Illustrator, like 25.2.3. Check this link if you want to keep a copy of both Illustrator versions to ensure backward compatibility:

  2. Or try to export any object as an SVG from File > Export As , then set the Decimal to 2 in the SVG options (as shown below). This will fix the Illustrator bug, and then try again to import shapes into Fontself. This should prevent the error until they fix Illustrator in an upcoming release.

FYI we warned Adobe and you can upvote this issue so they fix it sooner: https://illustrator.uservoice.com/forums/601447-illustrator-desktop-bugs/suggestions/43875663-copy-paste-vector-illustrator-figma-inkscape-gi