It's a hard one to nail down thats for sure. I watched Caren Armstrongs' tutorial on practice and she reminds us to slow down and get the technique/accuracy correct. I do this and like yourself don't seem to be able to transition to changing smoothly when I try to go faster than snail pace. Definitely harder from open chords to barre. I'm focusing on bm at the moment as well.

With other techniques e.g. open chord changes, picking melodies, blues riff etc this works well for me and I achieve actual results.

For some reason I'm getting tangled up with changes at barre chord time. I will keep at it at a slow pace and maybe one day it will all fall into place. I'm in my mid 50's so maybe it takes longer to obtain the muscle memory on some stuff 😉