SB Cam Thrust Plate P5249637 no longer made? Only tensioner now?

Duane said
Mopar performance used to sell a high strength cup washer for that because the stock ones used to collapse. So yes yours may have came loose.
No the washer does not control the end play. It merely secures the came gear to the came. The end play is control by the machining of the three components combined. The end play is probably just so oil can get between the parts.

IIRC the cupped washer flexes/preloads and provides a constant tension on the cam to prevent loosening. The Milodon torrington bearing is correctly positioned as the interior side of the cam is pressure lubed while the outside plate (under the cam cog) is sling lubed and there isnt chain sling from a gear drive.