Still cannot complete a snapshot or backup. Patrick and Nahid worked with me and we eliminated several possible issues. We could make a snapshot of Plugins alone, but could not complete a snapshot with even a basic theme (TwentyNineteen) and only WPMU DEV and Snapshot Pro activated. Dreamhost tech suggested we run PHP 7.2 rather than 7.0, and we agreed. Dreamhost also said there were no errors at their end, and the max_execution was 1500, but it looked like it was still at 500. Still, no one could determine why Snapshot and managed Backups will not work.