I don't believe this coin would be from the unreduced emission. Two things seem most likely- first, that a flan from the first emission was mistakenly used.
Secondly, and what most likely happened, is that it is just a heavier flan. The CONSERV coins from this emission were struck at 48 to a pound for an average of around 6 grams. Each flan was not weighed though, so some might be heavier and some might be lighter.
and a third possibility- the weight is misrecorded in the auction.
Drost in his book on Maxentian coinage only has the CONSERV coinage listed as reduced folles. He only gives an average weight of 6.47g and does not list weights of individual coins.