When Glyphs considers a glyph to be a “ligature”, it expects the anchors to be called something_1, something_2, etc. so that it can use mark-to-lig positioning to put the marks on the “relevant” ligature component.
However, U+05F0-05F2 are not strictly ligatures but digraphs. (They have no canonical decomposition in Unicode.) Marks on these letters should appear centered between the two stems, and I would expect to place a bottom anchor instead of a component-specific anchor.