I would say it depends on the content of the template. Using {{GER}} as template here works, but your template is more complex and contains a inner wikitable and than it is possible that the pipe of the closing syntax |} and the || is confused in the parser.

Change to table was in https://de.wikipedia.org/w/index.php?title=Vorlage:Hilfe/inputarea&diff=next&oldid=179808566 some days ago

{| class="wikitable"
|
{| class="wikitable"
|-
| inner
|} || second - this may confused the parser
|-
|
{| class="wikitable"
|-
| inner
|}
| second
|}

As far I know that was result of a fight against malfunction / bad rendering of a template that worked until July 2018 and now attempts to find a solution for correct rendering on 7th until 9th of August.

However, any number of pipes, double pipes and table closing |} should be parsed correctly if arranged in right order.

@Umherirrender – nebenbei hatte ich dich vor einer Woche in einem privaten Chatroom erwähnt – kam das bei dir an?

Indeed, the version of May 2018 has been wrapped into <div> rather than wikisyntax table, but that suddenly made problems as well.

Okay, terminating table with a line break should help here but may break somewhere else, let’s see what happens.

Thanks until now.

This strikes me as having likely been broken by Remex. In general, use HTML in templates, not wikitext, otherwise interactions like this may happen.