I think I’ve found a bug related to how Sen2Cor uses the SRTM DEM.
Specifically i think that Sen2Cor does not use any DEM if any SRTM tile that the S2 scene overlaps can not be downloaded. Because the whole function gdalDEM_srtm in L2A_Tables.py returns false if the download of any overlapping SRTM tile fails.
So where to report this? The github repository of @umwilm does not have a bugtracker.