DIAGNOSIS Yeah, this one's common. The mower deck is almost certainly clogged with wet grass, especially under that plastic cover around the blade. That turbulence kills airflow, so the blade can't lift and cut the grass blades properly—it just whacks them and throws them out the side.
FIX Unplug the battery. Tip the mower on its side (with the air filter side UP to avoid oil issues). Get a stick or a gloved hand and scrape out all the packed, caked-on grass from inside the deck, focusing on the channel around the blade and the discharge chute. It's usually a shocking amount of gunk. A hose can help, but let it dry completely before use.
IF THAT DIDN'T WORK With the mower safely tipped and the battery out, check if the blade is actually loose or bent. A wobbly blade won't cut cleanly. If it's nicked or bent, you need to replace it—it's a standard 20-inch length, but get the Ryobi part made for this model for balance.
HEADS UP Mowing wet grass or letting the grass get too long before cutting is a guaranteed ticket to a clogged deck. Try to mow when the grass is dry and don't take off more than a third of the blade height in one pass.