What are these weird Pringle-shaped plastic things that washed up on the beach?

On Reddit, u/SnapeSev reports the discovery of mysterious plastic disks that washed up on the Italian shore near Rogivo. They're flexible but hard and have the distinctive hyperbolic paraboloid topology of Pringles chips. The early bids: fancy packing material or biofilm substrates.

These discs are the same size (slightly smaller perhaps) and shape of a Pringles chip, and appear to be made of hard plastic, but are slightly flexible.
The discs started washing ashore in Rosolina Mare, a small coast town in northern Italy, near Rovigo, and have steadily continued piling up since the beginning of January.
They clearly come from the sea and resemble the small discs used in water filtering machines but they are not the same: they are compact, with no holes in them, just a "waffle" texture.

I just think they're neat.

Previously:
Review: American Standard 735125-400.020 Toilet Tank Lid
Dutch Masters portrait subjects clothed in foam packing sheets