The internal pin that fits into the bottom of the mast had rusted off! Thats' the small bolt like protrusion from the metal plate held in by four screws.
Definitely the reason I saw the mast moving with the sail furled and probably the reason the furling drum collar got pushed up. The bottom of the mast had nothing to ride on, but the plate itself.
I also noticed that the pin must have been hollow and appeared to be welded to the plate. The remains showed a cylinder, not a sold pin, along with clear corrosion. Weld failure might also be a possibility although I don't think so. The thing will have to be disassembled to find out.
That is 1/4" thick stainless plate and a 1/2" solid pin welded top and bottom to the plate.