The second issue is that I am still unable to boot into stock recovery and get the red triangle with an exclamation mark when I try to do so. I am running the latest firmware version (1.58.502.1), but was unable to find the recovery for that version, so I flashed 1.12.XXX.X. I have a feeling that this may be what's causing the problem.
I'd like to restore completely to stock. Can someone point me in the right direction?
After unsuccessfully attempting to convert my AT&T-branded HTC M8 to the Developer Edition (using the nandroid method), I ended up restoring to stock using the official RUU. I'm experiencing two mildly annoying issues that I hope someone can help me out with. The first one is not being able to change the CID back to AT&T's (CWS-001). I tried it a few times and fastboot returns the "invalid cid" error each time. I was, however, able to change the CID to SuperCID (11111111) without any problems.