Through several InDesign versions there is a problem with unintended page/column breaks. The bug is discussed in this forum thread:
https://community.adobe.com/t5/indesign-discussions/trouble-with-quot-mystery-quot-page-breaks-in-indesign/m-p/10838596
The workaround to remove Keep options and Balance ragged lines isn't a good one, I really need those options in a lot of my styles.
Sometimes it's enough to type a space at the end of the paragraph before the mysterious break for everything to pop back. This bug is a huge problem in collaboration with our InCopy clients who are not experienced users.
The bug is currently frequently encountered in both ID 17.4 and 18.0, but have been there for many years/versions.
I can't share any screen shots/videos since I'm working with sensitive information.