I tried to book BOS-MCO for 9/1 using a $50 eTCV earlier today. I found a U fare on Google, but all I was pulling up through the TCV redemption portal on DL.com was an L fare for about $40 more. I called technical assistance, and the IT person was also unable to find the U fare on the voucher portal. She ended up booking it for me directly, but without some behind-the-scenes magic, it wasn't going to happen.

I am not sure if this is related to the "unable to find low fares while logged in to SM account" problem. I was logged in at the time, but the IT person was not, and she still couldn't find the U fare through the voucher portal.