P0300 random misfire — already replaced plugs and coils, still misfiring

On the 2.4L Theta II engine, random misfires that persist after plugs/coils are often fuel injector related. These engines are known for carbon buildup on the intake valves (direct injection). Try running a can of CRC GDI IVD through the intake with the engine running. If that helps temporarily, you need a walnut blast cleaning of the intake valves. It's a 2-3 hour job.

Check your fuel pressure. A weak fuel pump can cause random misfires that feel exactly like ignition misfires. You need a fuel pressure gauge on the rail — should be 50-55 PSI at idle. Also check for any TSBs on that engine, Hyundai has had several for the 2.4 Theta II.

Had the exact same issue on my 2015 Sonata. Turned out to be a cracked exhaust manifold causing an exhaust leak right at cylinder 2. The O2 sensor was reading lean, the ECU was overcompensating, and it caused a random misfire across all cylinders. Weird cause but worth checking.