I'm not sure what to make of it. There are no plating bubbles anywhere else on this coin. It looks pretty solid and raised up higher than seated Lincoln.
Agreed; it's too smooth overall to easily believe it's a chip. With any Zlincoln, it's best to assume that if it looks like a bubble, it is.
plating blister...not all blisters are hollow, solid blisters are pushed up by gas under the expanding corroded metal...