As I mentioned here: https://community.adobe.com/t5/indesign/paragraph-bottom-border-overlaps-the-text/m-p/11348398?page=1 the issue occurs when I set a paragraph style with a border and additionally anchor a text frame at the end of it. The border overlaps each time changes to text are made (additional lines, adding a page, deleting a page – everything that causes the flow of the text).

Some similar issue was reported here https://indesign.uservoice.com/forums/601180-adobe-indesign-bugs/suggestions/38784706-footnotes-in-paragraph-borders-style by swapan.

InDesign version ID 2020 15.1.1 and PR Installer (15.1.2.221) on Windows 10. The problem occurs since I have started using a combination paragraph border + anchored text frame (more than 8 month ago). For testing I created totally new files with demo content (Lorem ipsum) and totally new styles created inside the new files. The preferences were reset.

It is easy to manage it manually when you have a single file and only one paragraph bordered. Making any change inside the paragraph adjust the bottom border. But when you have a book with over 30 files with over 30 problematic frames, it is hard to manage it.