I have an old house with lots of beadboard and wainscoting, and in my place it is inevetible that is separates in the dry cold winters.

If you don't want wood to behave like wood, then you should have installed MDF. You need a whole house humidification system for wood to remain stable. That includes AC use in the summer.

I have the same trouble with some book cases that are older.
I'm afraid I have to agree that it's the nature of the beast. Beadboard is usually thinner than ship lap, which doesn't separate (as much). I've learned to chalk it up to the "look" of older pieces.

I don't think you did anything incorrectly. Perhaps just installed at the wrong time? I tend to install in colder, dryer weather, so things are already contracted. I have to be careful not to install too tightly, or things will buckle. If I'm doing it wrong, shhhhhh! It's working on my floors and newer built pieces.

I put beadboard up in multiple rooms and then took it all down ~ 7 years later. Never again. Hard enough keeping all the trimwork maintained.

I should have mentioned that the beadboard is MDF, so it is not exactly like wood.

Glad I came across this. I've been considering installing beadboard in my new kitchen. Yikes, this makes me reconsider!

I've had the Nantucket beadboard in my bathroom for 3 years now. No separation at all! Did you get the SHEET product or the STRIPS? I went with the strips. Maybe that is the difference.