Riverdale spoilers through season 6 ep. 9 (ch 104)
Silly not real theory, except it's Riverdale so maybe??
Archie always had super powers but since they live right on top of palladium deposits it's been dampened most of his life. This is why he is still alive despite bear fights and numerous attempts to kill him.
Riverdale spoilers through season 6 ep. 9 (ch 104)
Hiram mining all the palladium in the town inadvertently removed Archie's weakness and therefore made him harder to kill, oops.