If I understood you correctly, files that wouldn't work from your F: drive yesterday suddenly started working today, even though you didn't do anything? This indicates to me that your problems are based on speed-of-transfer issues, as well as files not being ready to be used even though they may be visible in Explorer or File Open windows. Four clues lead me to that conclusion:
- Your SSD is much faster than your external drive, so read/write operations occur in a fraction of the time.
- You are only having problems with larger files (>45 mins. of video).
- The File is Ready for Archiving attribute only shows up when the file is completely written, has been checked by Windows, and is made available to backup utilities.
- PEK files allow Pr to draw the waveforms in the timeline, and for longer video clips this can take a few minutes.
My suggestion to you is to start transferring files from the camera to your F: drive (the USB transfer should be OK, but it's going to be slow), and while that's going on, go get a cup of coffee. Give all the file operations a chance to be completed by Windows before you try to import into Pr.
Jeff
EDIT: I should add that your USB setup is a huge bottleneck. If you think about it, the data has to go from the camera through a USB port (2.0 maybe?), out through another USB port to be written to the F: drive, then read back into the computer for playing or editing from that very same F: drive through that very same USB cable, all while the computer is still trying to write more data to the external drive. It's like a salmon swimming upstream.