Which snaphu did you apply?
Did you call it within SNAP, snaphu 1.4.2, ?
Did you apply the default parameters as this,
Or did you apply the latest version snaphu v.2.1?
Also, did you apply goldstein filtering?
Please take a look at this post,
SNAPHU: Statistical-Cost, Network-Flow Algorithm for Phase Unwrapping
Source: https://web.stanford.edu/group/radar/softwareandlinks/sw/snaphu/
In snaphu v.2.1 there are more parameters you could play with.
Also please have a look at the ,
TRAIN - Toolbox for Reducing Atmospheric InSAR Noise
Source : http://www.davidbekaert.com/#contact