MikeJones never seen that. I doubt it's caused by Flarum itself.
Maybe you or another website have a link to that page even though it doesn't actually exist ?
Analytics should tell you where visitors for that page come from. Is there a referrer website/page or a search engine ?
If it's direct access, it could well be bot traffic. I've seen some doing strange things. Check if the user-agent for those is promoting some unethical SEO company 😅 I suppose Google still hasn't got rid of them. I left Google Analytics because of all these junk stats.