What shows up in the submission confirmation email (the one acknowledging receipt of the wayspot submission)? The contents should go title, description, supporting text, main photo, supporting photo, location.
Since you do what I do (tbc and write them up later), it’s likely that that photo got misplaced as rhe main photo during the submission process (which glitched), as you’d have noticed a missing main photo while editing.
All reviewers would have seen would have been that photo with no supporting.
It’s unlikely Niantic can recover the missing photo due to when/where it went missing. Hopefully you can get back there to take new photos.
I had a review recently where there was no supporting photo. I think this is why the emails and Contribution Management are important, as if there is some glitch that could happen during the upload process, you can check the nomination to make sure that everything went through, and if not, withdraw if only 1 photo was uploaded.
Personally, I check my email and Contribution Management a few minutes after uploading to make sure my nominations have gone through correctly, but if there are any issues with the photos and/or location, I have the option to withdraw them and submit again, hopefully without any glitches.