Check for loose screws on airgun & scope mount.
If it’s like the 52 / 48, the outer barrel sleeve may have come loose, or maybe the muzzle weight / front sight ramp has come loose, which then vibrate & can cause POI shifts.
I’ve had similar problems from a broken mainspring, too, especially after shooting very heavy pellets. Is the cocking arm very easy to open for the first few inches, then gets firm like it should? When my 52's did that they had broken mainsprings.
I remember being in a friendly shoot off for cold beverages with my 52 topped with a Simmons Pro Air scope. My accuracy turned sour, & my reticle looked like an X instead of a cross...I’d shaken the internals loose (got it fixed & now use it on a pcp & it’s actually a pretty good scope). I never liked Bud Light, but liked it even less from then on (tastes / smells like CO2).
One other thing, I remember my cocking arm becoming loose & affecting accuracy. Mine loosened where the link enters the silver sliding cocking piece. Every now & then I had to cock the rig half way & snug up the hex screw that anchors everything in the rim of the silver cocking piece, facing the muzzle.
Man, I used to shoot the heck out of my 52’s (a 177 & two 22’s).
If you beat me in a beer shoot-off, at least make me buy GOOD beer..