Hi Lucas. My name is Oeds. I'm not with HTC, but am actually in a similar situation as you are, with 2 headsets and just starting out testing LBE mode.
The black image with the HTC logo loading is indeed happening whenever the headset lost / never had its tracking. When I walk into my testing set--up, which looks awfully similar to yours, I usually just hold the headset and point it in a few directions, and it picks it up.
Sadly, I do not have the answer as to why it is not working for you, as I said, your set-up is very similar to mine. We also have a dark floor, decent lightning and tape all over the floor. However, I did also have tape on some surrounding furniture, such as the closets. As far as I know, the headset will try to map any feature points around the environment, so perhaps it will help your case?
Best regards,
Oeds from EasySee