Settings of fretboard diagrams are lost in palettes (style issue)
I don't know how it's done. I created fretboard diagrams for Ukulele in v2 using Gimp, 4 strings. I've been using them for more than a year. I can load them in v3alpha2, and they show up correctly right after loading. But after restarting MuseScore, they are 6-string??? See image!