The connection in this period between Karaites and Sephardic Jews in a topic that requires closer examination.
Sephardim, whose Marrano outlook might lead them to consider rabbinic Judaism as a kind of deviation from biblical religion, would have found Karaism attractive.
The Karaites in Egypt have preserved a text that describes the arrival of some European Jews in Cairo in 1465.
The practices of these Jews, based upon the Bible, without support from rabbinic tradition, seemed more in accordance with Karaism.
A public controversy arose with the rabbinic establishment over the affiliation of these newcomers so that the matter ended up in the hands of the Muslim religious authorities, whose rulings are recorded in the text.
The subsequent involvement of Egyptian governmental authorities led to arrest and confiscations, and in the end the Karaites enjoyed a victory over Rabbanite adversaries.
The Europeans were permitted to convert to Karaism without hindrance from the rabbinic authorities.

See William M. Brinner, A Fifteenth-century Karaite-Rabbanite Dispute in Cairo.
The text is translated by Hartwig Hirschfeld in A Karaite Conversion Story, from British Library MS Or. 2538, fols. 73-83.
Other copies are found in the Jewish Theological Seminary of America in New York under the title סיפור ערבי (An Arabic story), Mic. 3328; and in the Blumenthal Rare Book and Manuscript Library of the Judah L. Magnes Museum in Berkeley, California, in an uncatalogued manuscript in the Karaite collection.

Fred Astren, Karaite Judaism and Historical Understanding, 223