Edit: lol I missed there were more responses as I had to step away and didn't refresh the page. Thank you for the updates! I'll leave my original response here anyway, and I do intend to see if I can have better line returns for errors.
Hmm, this seems fine to me. The custom.txt line is irrelevant; it's just checking if you've got the inline python tool installed and need linting for it.
How are you running the linter? From the launcher lint option, or from an in-game button? 8.2+ properly parses lines using the say_menu_filter, so you can run it from the launcher rather than the custom in-game button.
My other thought is possibly that you have an {else} split up across multiple monologue lines - these are considered individual lines when considering text tags, rather than one text block, so an {else} that was left open, then two newlines to begin the next line, will not continue the {else} tag.
I'll see if I can modify the linter to return an actual line to look at as well!