First, what happens if you, for example, boot without USB-Disk, then if the System is booted up sucessfully you connect the USB-Disk and restart the TVH Service? Does TVH recognizes the recordings now? Because i think it should do so.
Just to clarify, the location of the recording file, in your case the USB-Drive, is stored in the corresponding file under
(Old TVH Configuration Directory) = /home/hts/.hts/tvheadend/dvr/log/
or
(New TVH Configuration Directory) = /var/lib/tvheadend/dvr/log
If TVH can't find the location specified in the file because, as in your case, the USB-Drive isn't connected, it thinks the recording has been removed and your recordings appear under "removed recordings." Nothing is actually moved. However, if you were to reconnect the USB drive, as in your case, and then restart TVH, it should find the recording where it's supposed to be.
So, please recheck this 😉