When a template parameter does contain ##-{## string, connection between opening ##{{## and closing ##}} of this template is lost. The template is not identified as a template any more, and not expanded any longer.
Example: [[ https://de.wikipedia.org/wiki/Special:PermaLink/187691710 | real article ]] and [[ https://de.wikipedia.beta.wmflabs.org/wiki/Test-Templates | isolated test cases ]].
[[ https://de.wikipedia.org/wiki/Special:PermaLink/187659809 | April 2019 ]] an edit by a chemist has been made. At this time most probably it has been rendered correctly, otherwise it would have been reported.
[[ https://de.wikipedia.org/wiki/Special:PermaLink/186738543 | Invisible control characters have been removed by bot ]] in March 2019, but none has been placed between ##-## and ##{## before and might have influenced parsing.
<nowiki/> or HTML entity does remedy.
Editors of German Wikipedia discovered that on 10 August 2019.
rMW / includes/parser/Parser.php does mention ##-{## several times
* StringUtils::delimiterExplode() line 5235 as of December 2016
* in galleries line 5251 as of December 2017
* inside STRIP markers line 1190 as of 2008, harmless
None of these seems to be directly responsible.