Topic on Extension talk:Linter

What does this mean?

I think that Linter wasn't able to pinpoint which template is causing the problem, but only a selection of several templates

Indeed. Note that the problem might be caused by the template itself, or by the template call.

Look this error. The tagged field contains 21 templates, then I use this URL to query if these templates have linter errors and eventually I don't get anything.

P.S. I noticed Parsoid doesn't recognize the error in Lua modules.

If a template doesn't have linter errors, that can mean that the linter hasn't seen it yet, or that the errors aren't transcluded in the template itself. In any case you can use Special:ExpandTemplates to look at the generated wikicode. In the first few lines you can already see multiple unclosed font-tags obviously caused by Template:User rainbow.

For bot, the difficulty of repairs has increased. :)