backupwordpress not completing

I am using SiteGround + Zuperla theme + BUWP v 3.8 for several client and one in particular isn’t working.

When I run a full backup or database only it shows “starting backup” for a few seconds then stops and returns to normal status as if I never made the request. There should be no problem with server space and when I use developer mode console no errors appear. The only main difference between now and late January is that I started using SG Optimizer but even if I deactivate it now, I still can’t run the backups. And the other sites run fine with SG Optimizer.