Bill Tindall, E.Tn.
what temperature did you try "brushing" and did you try a foam "brush"?

I had no problem leveling a Target urethane kitchen finish using a foam brush at room temperature, probably around 75-78 F. I was finishing the frames in place in the summer, but air conditioned house and probably humidity in the 50-70 range. They came out glass smooth.

I did have to work quick and no going back once brushed. The successful technique was to load up the brush (3") enough to coat a stile or rail with one pass and work quick enough that the intersections of rails and stiles didn't dry till both were coated.