It is very frustrating to see that in LOTW there are 2 qsos with the same call, mode, freq etc. BUT the time is sometimes 30 to 45 seconds difference.
For example, I send 09:24:31, and the other station sends 09:24:00 and that already has a difference. However, LOTW says they take a 15-minute difference into account.
This will give you the message "no matching QSO in log".
That's how I see it Dave.
See my example:
73 Patrick ON6AT