Dry hopped? Hops contain enzymes. Look up "The Freshening Power of Hops" and "hop creep".
Yeah, and sugars, but it's a stretch to go there for this case. All reports of those eff3cts involve KARGE amounts of dry hops
My experience with my recent maibock with 0.67 oz Palisades as a dry hop:
5/28 1.062
6/3 1.019
6/25 1.019 stalled for 22 days!, added dry hops
7/3 1.017 fizzing again, racked to secondary
7/12 1.013 no more fizzing, bottled
Maybe that's a "KARGE" amount of hops, maybe not, I dunno, you be the judge. That's my experience though.