Until one knows something, at first anything and everything might fall under the category of "behaving strangely", so this topic does not cover that (otherwise it would need to cover anything and everything).
Here's the Cache
In fact it will start out covering only one thing, which is a small caching issue which occasionally occurs. Caching - as you may or may not know - is the practice used by programs / apps / software to make repetitive processes faster the next time you use them.
The problem will become evident when you are trying to edit something which seems to disappear when you launch the page builder.
To clear the cache, in the WordPress dashboard, go to Settings > Page Builder > Tools > and click Clear Cache.
No? Caching Plugin installed?
Sometimes that may not work. In fact on occasion it will break things completely.
Perhaps you have a caching plugin installed? If that's the case, then perhaps the cache needs to be deleted.
For example, if you have WP Super Cache installed (which may be the case if I built your website), go to Settings > WP Super Cache > Delete Cache button.
On the next page that loads, click Delete Cache. Try loading the page builder again.