mismatch between journal and contribution transaction ID
It’s 100% the same transaction. iATS reported they had an issue with Transaction ID numbering sequence for a portion of Nov. I’ll copy paste the Email thst went out to Partners:

Dear Valued Partner,
Please be advised that if your environment takes postbacks and/or runs morning download journals from the iATS system, your clients may have recently been impacted by duplicate transaction records caused by a logic error in creating and assigning iATS transaction ID's.
When did the issue occur? From November 18th to December 2nd .
Has the issue been resolved?
Yes. Our development team has identified the root cause and made the necessary coding changes to correct any duplicate iATS transactions importing into your environment. We can confirm that this was due to our logic in creating/assigning iATS transaction ID’s and did not impact the number of transactions charged to account holders. This has been corrected and should not occur again, but as always, please keep us informed if you see any instances of this occurring.
What should you do?
There is no update needed on your part to correct the coding in order prevent this in the future. Clients are free to delete the duplicate iATS transaction from the environments without worry of impact. Note, clients should check the iATS portal to confirm which iATS transaction was processed and which one was the duplicate needing to be deleted.
If you have any additional questions, or should you need assistance in identifying these duplicate transactions, we are happy to assist you, or our mutual clients directly. They can reach out to our iATS Customer Care team for assistance with this process at iatscs@iatspayments.com or via phone at 1-888-955-5455 Option 1. 
Sincerely,