AUO, Chabad clearly and explicitly rejected the idea of moshiach being dead for years. Then the Rebbe died and suddenly this is Chabad belief?
The Rambam clearly rejects it as well. Chabad does Rambam Yomi and the Rebbe considered the Rambam so authoritative that the distinctive Chbad menorah was based on the Rambam illustration.
Yes, there are a few sources for it. But it wasn’t mainstream, and the Mechaber clearly stopped believing in Shlomo Molcho once the Christians killed him.