Go to

https://en.wikipedia.org/w/index.php?title=Formal_criteria_for_adjoint_functors&oldid=963936645&veaction=edit

and click on the math theorem template (the bounded box), then click on "Edit" to edit the template's contents. Make a trivial change, e.g. add a space somewhere, and click on "Apply Changes". You will notice several bogus <nowiki>'s in the bounded box (under points 3. and 4.) that don't belong and weren't there before.

If you edit the template again, or save the page, the nowiki's are gone, so this is purely a presentation issue during preview.