Lines grouping together even though they have returns causing gaps

[Holeycow]

I'm having to deal with a problem that I haven't come across in 20 years of using InDesign.
A client has supplied a file where, for some reason, lines randomly seem to want to group together which creates white spaces mid-sentence at the bottom of a paragraph.
I've tried various workarounds, such as rewriting the passage and pasting it in, but nothing seems to get around it.
Has anyone else encountered something like this and found a workaround?
I'm suspecting the problem may be in the clients original file which is a 120k word book.
I've attached a couple of screenshots to try and help explain what I'm talking about.

[Peter Kahrel]

It looks as if single-line paragraphs have keep with next and keep with previous applied to prevent those single-line paragraphs from appearing at the top and the bottom of the page. Can you check that?

[Micah5C08]

That sounds like a keep option... go to this page in the paragraph style and try unchecking the checkboxes

[Holeycow]

I'd looked there... then looked again. No boxes were checked, but it was set to 1 line rather than 0... thank you. Problem solved

[Peter Spier]

You might want to keep at least two lines together at the end of the paragraph to avoid orphans (single line paragraph endings at the top of a page)as shown in your first screen shot.

That dialog is confusing, to say the least. Though they look like they are related, the Keep with Previouos checkbox is a separate function from the Keep with Next  field below it (those two together control whether multiple paragraphs must, in some fashion, "stick together"), which is completely spearate from the Keep Lines Together section that controls how many lines in a paragraph must appear at the top and bottom of a column.