Everything moves, especially wood. Learn how to use a moisture meter! Learn how to anticipate wood movement! And learn how to accommodate wood movement in your work.
Here's a link to an article in THISisCarpentry.com that should help!
https://www.thisiscarpentry.com/2010/...

And here's another link that dives into solution for movement in exterior trim:
https://www.thisiscarpentry.com/2017/...