It started out as intermittent I/O errors, where the system would boot fine and run for a few hours and then lock up to the point where I could not even SSH into it. I tried replacing the cables and connecting to a different power cable but the problem remained.

Within a couple of days, the drive stopped being detected. I tried one last time using an external USB3-to-SATA enclosure but got the same outcome. I'm guessing that the controller gave out, as the wear level stats were fine last time I checked (a couple of weeks ago).

This was being used 24x7 for the last few years as a boot drive for my Proxmox server, for which I run nightly backups so I was back up and running within an hour or so after replacing the drive.