My desktop system has a dual hot swap 2.5" bay. For a while I've had a Toshiba THNSNJ512GCSU (512GB SSD) in one of them. For some reason, the activity LED on the hot swap bay no longer shows activity when the drive is being accessed. The drive still works fine, and I just tried another drive in that bay, and the activity LED works normally with the other drive.
Weird.