Did you take the keyholes off when you refinished it? And did you then re-install them upside down?
I ask because the standard disassembly procedure is the lift the seat from UP, which is the same as pushing the arm down. This is so that you can lift the chair up from any other part, like the arms and it stays together. If you installed the keyholes upside down, the chair would come apart when you lift the arm up.
It's literally a matter of degrees and trial-and-error. The keyhole fixtures are ramped. If the screw is too tight, it won't fully seat. If it's loose, the joint will be, too. I can't think of a better application for the proverbial rubber mallet. Tedious, yes, but keep at it and you should achieve desired results.
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