no CEL or codes? get it scanned with a vag-com first just to check for any possible faults that have been logged.
i'd maybe start with checking the ATF fluid levels and maybe doing an ATF fluid and filter change. Don't do a power flush, just a simple drain, new filter and new fluid. And use the correct fluid. Pentosin can be found online at places like ECS Tuning or at your local vw dealer.
also check your engine, transmission and snub mounts. if these are failing then things can get out of line just enough to affect how it's shifting. perhaps the torque placed on the engine during a hard acceleration is actually bringing things into better alignment for shifting vs. a normal/moderate acceleration.
these would be your least technical and invasive places to start.
could be other internal issues with the transmission or maybe a flaky TCU starting to give after suffering from a bit of un-noticed water ingress.