Dear S2TBX team,
S2Tbx allows to visualize easily viewing angles (zenith/azimuth) corresponding to a given product.
I suppose this field is computed from one of the viewing angle grids provided in the granule metadata for each spectral band.
The issue is the following: when a grid point falls out the instrument swath, the value is NaN in the product grid, which corresponds to No Data. However in SNAP a value of 0 degree is displayed, which can be misleading. It should be displayed as No data.
the S2 Mission Performance Center is currently investigating a change of the definition of these viewing angles.