For non-ligature glyphs, you should get the anchors from the last component they show up. I just tried the DZ in Glyphs. The D and Z have a "top" anchor so you get the one from the Z. The D has a center anchor (for the bar to make a "Eth"). As the Z doesn’t have a center have it, you get the one from the D.
https://github.com/googlefonts/glyphsLib/issues/368#issuecomment-2103376997