Hi @dspreadbury,
I just tried a possible workaround.
- I activated the Beam Groups setting in the MusicXML import preferences and imported the MusicXML file. The double note tremolos was imported.
- I choose Select All and then Reset Beaming to get Doricos beaming rules.
I think this really should work. BUT, when I do the reset the imported double note tremolos disappear from the score. This is true even if I create the double note tremolos in Dorico (not just the imported ones).
Conclution
It seems like Dorico represents double note tremolos as beams even though they are not. That sort of explain why single note tremolos are imported (as they are not treated as beams) and why the Beam groups setting affect the double note tremolos import but really shouldn’t.