Official comment
It is hard for us to tell since we don't see any maps with issues in your account.
If there is a problem with the upload or the source imagery it is always best the cancel the upload before the job starts so you are not charged for processing bad data.
If a photo is all black for some reason it will likely just not be included in the output. You will still be charged for processing it. Your overlap will likely be affected by having blank data.
Please do not create duplicate accounts to get more free processing. Duplicate accounts are at risk of being deleted.