CirrusSearch does not seem to index "proofread-page" content model anymore. This content model is defined by the ProofreadPage extension and is used by the Page: namespace of Wikisource.
Problem first reported here (in French): https://fr.wikisource.org/wiki/Wikisource:Scriptorium/Mars_2019#La_recherche_sur_l'espace_%22page%22_n'aboutit_plus