I too had the exact same problem yesterday. Lost about 65 gigs which was one long clip. First ran Prosoft’s Data Recovery and it was not found although it pulled out older QT’s that since have been erased. Just bought Disk Warrior on Sound Devices suggestion but it will not run on my MAC since it is a Windows formatted SSD drive.
Very upset with Sound Devices, I just found out last night that they just released 3.5 firmware on the 5th that can help prevent a loss but I they neglected to tell me of the available update!
Waiting to hear back from Disk Warrior as to a suggestion before I pull out even more cash.