Try turning the barrel adjuster to your rear derailleur a tiny bit (1/2 turn) and shift through the gears. See if it helps. If it doesn't fix it but doesn't make it worse, twist a little more. Don't twist it a ton though, just 1/4 to 1/2 turns at a time and shift through. If it makes it worse, turn it the other way.

Could be a simple way to solve the problem.