What is the problem?
Attempting to switch to the Visual diff on the below page returns an API error:
{"error":{"code":"internal_api_error_UnexpectedValueException","info":"[6e110713-56d6-405b-87f9-7096378d4dfd] Caught exception of type UnexpectedValueException","errorclass":"UnexpectedValueException"},"servedby":"mw-api-ext.eqiad.canary-6fc68c567-6g5ht"}
I don't have access to logstash so I don't know what the full exception message stacktrace is.
Diffs where I can reproduce this include most of the diffs for this page https://www.mediawiki.org/wiki/MediaWiki:Gadget-BugStatusUpdate.js, e.g. https://www.mediawiki.org/w/index.php?title=MediaWiki:Gadget-BugStatusUpdate.js&diff=next&oldid=1408359
I have yet to find other pages where this happens.
Steps to reproduce problem
Observed behavior: You will see a red popup with the above exception.
Environment
Wiki(s): https://www.mediawiki.org MediaWiki 1.41.0-wmf.26 (f511adf) 00:18, 12 September 2023.