I just had an odd experience recently (as in yesterday) and this thread didn't help. however, I found something new that might help other ppl.
A brief background, I took a backup from my first S5 (now being utilized by my wife) then copied the files from the phone memory to the SD card. After setting up my second S5 (flashed then root process) copied the backup files from SD card to the phohe memory. But when I ran TB it can't find/detect the files, so meaning I wasn't able to restore anything. What's odd is I didn't experience this when I first setup my wife's S5, all went very smooth.
After many hours of digging I finally found a solution (in my case, at least). All I did was to rename all the backup files with extensions .gz.zip to .gz and wallah!
Hope this helps.