Text Box

@Kylee5E1B, you've got your answer(s) - but just to clarify something - what you are talking about is a Text FRAME - Text Box is something else, in the UI it's is called "Text Field" and in scripting TextBox.

Text wrap is usually pretty simple and absolute; if there are complex algorithms that try to keep words together or such, I'm not aware of them.

But there are several factors that apply to text wrap. Spacing on the right side of text, or spacing on the inside margin of text boxes, can have unexpectedly "fussy" effect on wrap. Check both and try not to combine them  — if you have, say, a 1 pica inner margin on a text box, don't use any right spacing on the content text that it might 'argue' with.

Hyphenation control can also (slightly) affect word wrap as it tries to maintain the fewest number of hyphenations and/or limit stacks of them. Turn hyphenation off and see what happens. You can also tweak hyphenating rules quite a bit if you need hyphenation but need to minimize or adjust its impact.

A very general comment, though — you typically do not want to break text and content up among multiple text boxes. It's best to use one text frame per page and then use Paragraph Styles to manage how the text spaces, positions and flows. It's poor practice to use text boxes to position and manage text. (Maybe that applies to you, maybe not — reading between the lines of your post, a bit, here.) Using styles for management allows ID more flexibility in applying all of its layout and adjustment rules.