Sep 2 2020
This might be a separate issue, but it appears that XTools is case-sensitive when it comes to article assessments - see for example https://xtools.wmflabs.org/topedits/en.wikipedia.org/David%20Eppstein/0 where you can see that "Start" and "Stub" are considered valid classes, whereas "start" and "stub" are not, despite the fact that the WikiProject templates don't care. You can also see this on the article info page: https://xtools.wmflabs.org/articleinfo/en.wikipedia.org/Smooth_number#assessments https://en.wikipedia.org/w/index.php?title=Talk:Smooth_number&action=edit
Sep 1 2020
Jun 11 2020
Working for me on en.wikipedia. Issue started at roughly 18:36:49 per recent changes.