Just keep at it. I took me a couple weeks and then I was at the point where I could easily switch back and forth. But I had the same thing where after the first few weeks of using ortho, I had some issues going back. But they went away pretty quickly. For a little while I kept trying to switch back and forth each day, but not sure if that helped. These days I'm mostly moonlander, but when I'm traveling or on a plane, I may just us the laptop and my brain/fingers just know what to do.
So, basically, keep at it and you'll be fine.
I prefer fully split keyboards overall, but every time I go back to using my Atreus I'm reminded what a nice keyboard it is, and how lovely it feels to type on it. Those guys know what they're doing.