Spacing is correct for the first couple of hundred 1.5 spaced liberation mono lines, but then they become wider and none of the 1, 1.5 or 2 line spacing options correctly place them.
The line spacing is specified in the paragraph template.
It can also be specified via the Format > Paragraph menu.
However, if possible, a paragraph template should always be used.
You have probably used different settings.
Place the cursor in a paragraph and look in the sidebar on the right to see which paragraph template is displayed.
Use a uniform paragraph style for the text (without headings).
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If you have taken text from other sources, you can never know the format of that text. Once you’ve pasted it into Writer, highlight it and choose Format> Clear Direct Formatting (Ctrl + M). You can now assign the desired paragraph style.
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Here’s how to assign paragraph styles:
https://wiki.documentfoundation.org/Style_templates_in_Writer_-_V6
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With me Windows 10 Home; Version 1909; 64-Bit | LibreOffice, Version: 6.4.1.2 (x64).