I've tried on LO 24.8.4.2 on Linux and can't confirm your test: here it seems ok. Did you check paragraph style and character style?
I've Googled this and all the results say this .... https://ask.libreoffice.org/t/how-do-i-change-my-line-spacing/9807 To change to single spacing - Format > Paragraph > Indents & Spacing - change Line Spacing to Single click OK. The text remains double spaced. Even when I checkmark Activate Line Spacing - same result. If I place the cursor at the end of a line and hit Enter - it re-positions the cursor 2 lines down, not one. Miss those WP reveal codes.
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