This question, titled How did ancient China invent such wonders as fear systems and calendar before ancient Europe? has been removed and the 404 it leads to contains a list of some similar questions that might be relevant. Oddly enough, the aforementioned list again contains the removed question. Further, the "related questions" suggestions on the right side column on different pages also contain the deleted question.
Judging by the "id" (or whatever else that number xxx in the URL format
topic.se.com/questions/xxx/question-text is called) of the removed question: 35044, and assuming that these numbers increase over time, it is not a very recent question, at least a few months old. So this is most likely a bug, not a caching issue.
Naively, the most straightforward solution would be to have the database query that generates the list of related questions also check the field for whether a question is removed.