The lemon oil products like Gellespie are for cleaning and conditioning finished furniture so using prior to your topcoat was probably a boo-boo. The good news is that it does not seem to be your issue as the problem is isolated to a particular area. Poly, by nature, is not something that "buffs out". It is soft/tough and formulated to resist abrasion.
I think I am hearing you say that even if you recoat the area, it remains dull(?). A picture would tell a thousand words on this as it could be that you are using a gloss finish and have a contaminant in the area. You are using a satin finish and did not stir frequently during application and you got a brush full of concentrated solids that left a streak of "dull" in the finish. Really too many ways to guess about this. How about a picture?
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