What was the weather like when you applied it? If humid, raining or cold outside it won't cure. Was it stirred slowly and completely? That is another reason but the main reason is humidity and air temperature.
It could be so many things!
The wood types being different could make a difference depending on soft v. hard woods (more common a construction trick than people realize), and how 'dry' the woods were.
Was the humidity level in the area different when you applied the poly to the top as opposed to when you did the leaves? That would make a huge drying time difference. Try placing a large fan in the room to move the air and take out some of the humidity. Try to place that fan so that it moves the air rather than blows directly on your work-you want to avoid dust becoming one with your work:)
How heavy was your application on the top of the table? It's pretty easy to over-apply a coat to a large surface and that will take much longer (up to over a week) to completely dry.
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