In case you have not noticed, you can request deletion of notes on Amethyst, and that is what you get....
It's one explanation.
Also if the note is posted under a relay you don't have in your relay list, it can happen, also.
Second explanation.
Discussion
I checked that my Amethyst setup includes all the same relays that are listed in my Primal setup. But the deletion thing might be relevant yes; it seems like support deletion (and editing) varies across clients. Thanks for the input!
Anyway, another reply suggests that it's about caching, and that the next version will fix it
Much appreciated 👏 💐