Navigating to Special:CiteThisPage shows an error page for blocked users/IPs whose title is "User is blocked" (blockedtitle). This is unexpected, because blocked users should be able to use the tool to cite pages.
This issue has been reported on https://fr.wikipedia.org/wiki/Wikip%C3%A9dia:Questions_techniques/semaine_46_2016#Blocage_et_.22Citer_cette_page.22, and I was able to reproduce it on fr.wikipedia.org by using a globally blocked IP.
I believe this is related to the change https://gerrit.wikimedia.org/r/313557, which was done to solve T147046: as far as I understand, FormSpecialPage does not allow blocked users to run execute() unless requiresUnblock is overridden.