When Create Backup Download fails, there is no indication anywhere that I could see. I had it fail on me three times in a row now for a large-ish client site – got the «here's your download link» mail once, after 24h or so wait time, but the link was expired by the time I got it. The other two or maybe even three times I started the process, simply nothing happened – no mail, no indication if it was still working on it or if it stopped. Plugin/Theme/Core «safe updates» also could use better signalling in case of failure. While the process is running, when an update fails, there is a red indication and a «Attention needed» text (that looks like a button, but does nothing) – these simply vanish after a few minutes, making it look like everythings fine... unless one looks quite closely.