Some examples are:
From dewiki:
```{{subst:#ifeq: {{{2}}} | a | style="line-height: 15px; background: #DDA; border: 3px solid #A86;" | {{subst:#ifeq: {{{2}}} | b | style="line-height: 15px; background: #DDE; border: 3px solid #1874CD;" | style="line-height: 20px; background: #E0E0E0; border: 2px solid #1874CD;"}}}}```
From plwiki:
```{{państwo dane {{{państwo}}} | infobox państwo/core | wariant ={{{państwo}}} | link | altlink | nazwa |rozmiar }}```
Discovered this via infinite loop expansions on some pages:
plwiki/Wikipedysta:Matma_Rex/LOT_Flight_165_hijacking
plwiki/Wikipedysta:El_Slavco/brudnopis
plwiki/Wikipedystka:Wakashimazu/Impuls_Arena
and {{Begrüßungsbox}} transclusion on dewiki.
We should investigate and fix. The infinite loop itself exposed a different bug that is now fixed via https://gerrit.wikimedia.org/r/#/c/189036/. But the original cause of failed expansions is tracked here.