Disallowing widows in InDesign causes breaks in the middle of the page

I've run into this same frustration before. It usually comes down to InDesign trying to resolve conflicting rules. If you have 'Keep with Next' enabled on a heading or a style in the middle of that text block, the engine will prioritize keeping that block together over your widow/orphan settings, which leads to those weird mid-page breaks. It might be worth checking your 'Paragraph Rules' as well. If you have a rule above or below that has a high offset, it can essentially act as an invisible line that triggers a break prematurely. Have you tried disabling 'Keep with Next' temporarily to see if the text settles back into the frame properly?

It might be a glitch - it’s hard to confirm that for you for sure, without a sample file or a video of the potential glitch in action. I’m inclined to believe that Eugene is correct, and that you might have Keep Options turned on in places you don’t know about. Additionally, having No Break turned on in places you don’t know about can cause this kind of behavior. But text composition glitches aren’t unheard of, especially when e.g. working in an up-to-date installation of InDesign, on older files that were created some versions back, with a history of version-upgrade file conversions. I’ve been running through these steps a lot:

1. I see weird behavior - line wraps in an unusual location, paragraphs with hanging indent style applied rendered without the hanging indent, et cetera.
2. I say “Huh” and hit the keystroke to Recompose All Stories. That’s Ctrl + Alt + / on Windows; I think on Mac it’s Command + Option + /. That fixes it for me, maybe 20% of the time. Or, if it doesn’t:
3. I Save a Copy and open the copy, or maybe I export to IDML and reopen. This fixes it for me, again about 20% of the time. Or, alternately:
4. I click the “Reset preferences on exit” button in the Preferences dialog, and restart InDesign. This fixes it, maybe 40% of the time. 

Have a look at the Keep Options in your paragraph styles.

For regular body text, Keep with Next [X] Lines should generally be set to 0, and Keep with Previous should be unchecked.

For body paragraphs, you can use Keep Lines Together > At Start/End of Paragraph to control widows and orphans, typically setting these to 2 lines.

It's usually headings and subheadings that need Keep with Next, so they stay with the first few lines of the following paragraph.

I suspect you have some body paragraphs with Keep with Next enabled, possibly through a paragraph style. This can cause entire blocks of text to jump to the next page because InDesign is trying to keep those paragraphs together.

I'd check the Keep Options in your paragraph styles first, as that's likely what's causing the issue.

You may have a return somewhere that’s dangling, like halfway down the next page. 

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