I don't recognize the use of {} in the comment. Can you use value-of
and select the result? I'm outputting text not xml, so the comment
wouldn't work.

That was XSLT 3 with a text value template (expand-text="yes"), but it
doesn't matter, of course you can use value-of.

At least as long as you use the variables in some way that you allow us
to reproduce the error.