I finally figured out my problem (i.e., why I couldn't get Channel 6002 for WNYW New York's O&O Fox station back in my TVE YouTube TV source lineup). I must have somehow deleted just that 6002 station when troubleshooting, and tried multiple rescans and never got 6002 back (no error message, it just never came back). I finally deleted YouTube TV as a source and tried to re-add it, and I THEN saw the error message about Google blocking the authentication process. Did a little more digging in the blogs and realized that running the Channels DVR server on a Raspberry Pi and trying to use TVE with YouTube TV credentials no longer works.
I pulled an old MacBook out of the closet, installed Channels DVR server on it, moved my external hard drive from the Pi to the Mac, and was able to get back ALL my TVE channels (including 6002) using my YouTube TV credentials.
Unless I'm missing something, the Channels development team should really make it obvious and clear that YouTube TV TVE with the DVR server on a a Raspberry PI just doesn't work anymore.