Why would solder paste not wick in completely during reflow?
Solder wetting and wicking is generally a function of successful flux.  This removes oxidation and generally makes soldering possible.  It also lowers the temperature at which the solder flows.  (This is one property that can be exploited with double sided components when oven temperature can be enough to re-flow the top without remelting the bottom.)

You have too much paste and it is either too old or exposed too long.