I have a problem with a glyphs file that hasn’t been edited for a while now. (I can’t say more precise, e.g. regarding the version number.)
After one of the last updates, some accent components are no longer “connected” to the anchors, i.e. some do not respond to “move”/place. (In one master it works, in the other not. The next glyph is the other way round.)
Automatic alignment is off. Recompose the glyphs or reenable alignment.
Most likely explanation: Opening an old file in a new version should give you a dialog box about what to do with marks that are not exactly where they are supposed to be according to automatic alignment. Perhaps you chose Keep when you came across that dialog.