Yes, hard drive doesn't seem to be the culprit. The office camera that I moved to that drive seems to be writing fine. This is on a new SATA controller so I thought that might possibly be the issue, but it seems good.
Neither drives has any clips from the offending camera. I deleted and re-added the camera this morning and it still is doing the same thing. Long name of the camera is "Living Room" and short name is "LR". Previously it was "Living Room 2" and "LR2" as I had another camera using the current name earlier today. (I added this camera alongside my old one. When I noticed it wasn't writing any clips, I deleted the old cam and new one and re-added the new cam with the name of the old one.)
All drives are internal. The drive I moved the offending camera to is not new and has a couple of other cameras writing to it.
I've attached caps of the status and the file format and compression screens. Seems odd that there doesn't seem to be any sort of error or alert message anywhere.
Thanks for all your help.