I saw this noted on enwiki's Village Pump: Nowiki bug in Visual Editor.
In this diff, it looks like every pipe was padded with <nowiki> tags.
Hmm .. this looks strange. Knowing nothing else, my first guess would be that this is probably a Parsoid client issue returning bad HTML.
This edit was made in the VisualEditor-MediaWiki-Mobile
Here's another example: https://en.wikipedia.org/w/index.php?title=Government_of_the_4th_D%C3%A1il&diff=next&oldid=989679089
That is also a VisualEditor-MediaWiki-Mobile edit. So, my hunch is that something is messing up the HTML in that tool usage in some cases.