Example: https://xtools.wmflabs.org/pages/en.wikipedia.org/Piotrus and article https://en.wikipedia.org/wiki/Adulting . Assessment is displayed as 'unknown' even through the article's talk page has a correct |class=stub parameter. There is probably something messing this up due to the tag being partially suppressed; analyzing the code at https://en.wikipedia.org/wiki/Template:WikiProject_Culture may help find the issue.
Topic on Talk:XTools
The issue appears to be with Template:Inactive WikiProject banner, but I can't help but wonder if this desired behavior. One could argue that if a WikiProject is defunct, so are its assessments. w:Template:WikiProject Culture similarly does not reveal assessments for defunct WikiProjects, nor does it put the page in any categories.
I don't think this is desired, assessments are often done by people who are not project members. A project does not have to be active for assessments to still be useful to thers. Assessments are in the end part of an all-wiki imitative, just 'farmed out' to projects for categorization. An inactive wikiprojects should not cripple the global assessment initiative.
I don't disagree, but regardless there's nothing to fix in XTools. Template:Inactive WikiProject banner does not accept "class" or "importance" parameters. It needs to pass them to the Template:WPBannerMeta parent template in order for the assessment data to be stored in the database. Basically if it doesn't show up at Special:PageAssessments, it won't show up in XTools. However to me it logically makes sense to omit storage of assessments if we're not showing them in the template, which is the case here.
The quick fix would be to simply tag it under a different WikiProject, perhaps the parent WikiProject Sociology. To your point about "the global assessment initiative", I concur it would be nice to have a more generic assessment system without the need for a specific WikiProject. After all, most WikiProjects seem to define classifications in the same way, at least up until GA or FA.