Sounds like a great find. To me, this isn’t weird at all since it’s a new motion. You might have a handle on it, but maybe it’s still new enough that introducing fretting is sort of “pulling” the motion back to your default motion. It’s like trying to brush your teeth while you comb your hair.
Back when I was being stubborn (well, I still am stubborn) and rebelling against my default fast motion, I really wanted to learn a USX motion. Because, ya know…Eric Johnson. Anyway, after a decent amount of searching and practice I could get the gypsy-ish motion going really fast for a tremolo. The minute I introduced some fretting that motion would go right back to what I’d always known, some wrist (or wrist + elbow) DSX. To be honest, I still need to warm that motion up and and concentrate really hard to get it to “stay”. Being aware of it helped. I’d devise little licks or etudes or exercises to help transition from a tremolo to the more “synced” fretted patterns.
Not sure what the equivalent would be for DBX since “tremolo” doesn’t really work (hard to tell if you’re doing the motion properly when it’s just on one string). Maybe a pattern where the fretting is doing something but not a ton, that way you can really concentrate on getting used to what DBX feels like. I’ve been on and off working on Tumeni Notes and one of the immediate problems I identified is that the fretting is pretty tough. So I made this little etude that has the same picking, but much easier fretting (and no muting at all, just let ring on a clean channel or acoustic) and that way I can make sure the picking is as efficient as it should be.
A few swipes but no big deal because the speed is getting closer to the “real thing’s” tempo and I think the fretting hand challenges were holding me back, allowing the right hand to become a little lazy and do a motion that while still not string hopping, wasn’t maximally efficient.
I guess the disclaimer on any of that advice is that we’re assuming your assessment is correct about the motion being solid when you remove any fretting. If you want to upload a clip of that, it could help confirm. So far I’ve learned USX, DSX (which I could always do) and DBX. USX took longer but my approach was not as smart as the way I learned DBX. I’d consider the latter to be the CtC-approved “happy path”. That said, I can see why DBX gives plenty of people a fit, just because if you’ve never done that motion before, it’s really hard to “find” it because the it feels so much different than the single escape playing. At least for me! The only thing I think it has in common with the single escape motions is the general feeling of “easy-ness” when it’s done correctly.