I confirm that this is related to the mentioned change of the location of SRTM 3Sec data.
Even if you have used another DEM during the interferogram formation (for topographic phase removal) SNAP still wants to access the SRTM 3Sec database in the StaMPS export, and the export will fail or stop to proceed.
So if you encounter the problem during the StaMPS export, please update the URL of SRTM 3Sec and delete old and incomplete files as described in this post until this is fixed by an update: