Here's proof that the pellets are starting out life badly. They are slamming into the side of the barrel, and smearing badly. This throws them out of balance and imparts a wobble.

These were recovered in a bucket of water. So even though the pistol was sent back for repair, it is still has the same issue.

Notice that the lower part of the pellet is not a true cone. This is because the pressure provided by the CO2 gas expands the soft lead. Pellets are hollow.