+ AA6YQ comments below
Tried a couple of QSOs. No change in the LotW sent field, it remains U.
+ OK. Please do the following:
1. On the "QSL Configuration" window's LoTW tab, check the "Permit uploading of QSOs already uploaded to LoTW" box
2. Right-click the Log Page Display entry for the same QSO you just checked, and select "Upload to LoTW" from the pop-up window. Wait an hour, right-click the QSO's Log Page Display entry, and select "Update from LoTW"; any change in the QSO's "LoTW QSL Sent" item?