Why is my chain hitting this one tooth on the smallest cog?

This appears to happen only on the smallest cog, on one tooth, on one particular segment of the chain. When the wheel is spun backwards, the chain catches on one tooth of the next cog up.

The groupset is Ultegra Di2. Brand new bike <20 miles

~~Is the derailleur perfectly aligned under it?~~ Edit: Oh, shouldn’t have any effect on the chain running on the top.

With new cassettes I’ve had this happen because the shifting aids are so aggressive that they grab the chain ever so slightly even when it’s perfectly aligned.