Remove the chain and have a look at the drive sprocket. It likely has a T shaped groove worn in it, time to replace. If it is the floating rim type, replace the rim.

And make sure the oiler is working. Steve

I'd take the bar off, clean out the grove and oil hole, and make sure the oiler isn't plugged. While you're at it inspect the sprocket for wear.
Is this a new chain? .325, .375, and .375 Lo Profile won't interchange.
When you put it back together you can test the oiler by putting a piece of cardboard on the ground and running the saw. You should see a spray of oil left on the cardboard.
Is this an Intenz bar or a conventional bar?