We used Behr paint on our walls and it seems to shrink away from the baseboards as it dries.
Yes it does, as the solvent evaporates. The shrinking is in the film thickness and shouldn't pull away or shrink away from your base boards. But in your case something else is happening.
Something is on your base boards and up the wall that is reacting with the paint. This could be cleaners, hair spray, polishing oils, air freshener oils from a spray can, etc. Recommend priming next to your base boards with a shellack primer then repainting.