That should not happen. You'd have to describe how you are restoring and any details on your backup plan.

Using Ultimate edition

From the Cloudberry Explorer (S3)
“Avatar.mkv 32.2 GB 1/24/2021 7:26.22 PM File Standard”

The resulting restores on my desktop
Avatar.mkv.part_1 9/2/21021 10:09 AM Type: PART_1 File 6,761,153 KB
Avatar.mkv.part_2 9/2/21021 11:09 AM Type: PART_2 File 6,761,153 KB
Avatar.mkv.part_3 9/2/21021 08:42 AM Type: PART_3 File 6,761,153 KB
Avatar.mkv.part_4 9/2/21021 08:42 AM Type: PART_4 File 6,761,153 KB
Avatar.mkv.part_5 9/2/21021 08:42 AM Type: PART_5 File 6,761,153 KB

• Chunk Size 10 MB
• Thread count 6
• Process Priority Normal
• Memory Automatic
• Unlimited disk usage

Single file restore plan:
• Restore from latest version
• Selected the video from the S3 cloud
• Set the restore location on my desktop
• Ran the restore plan

I must be doing something wrong (or something stupid)

You cannot use Explorer to restore most Backup files. You need to restore using CloudBerry Backup. Create a restore plan and select that file for restore and the location for the restore and you should be good to go.

I did not make this clear, but I used the Restore Plan. I only used the Cloudberry Explorer to verify the size of the original backed up file.

What do you see when you restore from CloudBerry Backup and select the file? Do you see all 5 parts as individual files or do you see a single file as it was on the original hard drive? If you see 5 files, then is it possible you split the file yourself before it was originally backed up? If it is simply split, you can probably recombine from a command-line using the Windows command-line COPY command COPY /B file.part1 + file.part2 FinalFileName

I will try a clean restore and then try to combine as you suggested

It appears that the files that I tried to restore from S3 were corrupted and/or damaged. I am backing up the files again. I believe that the problem is solved. I appreciate the help....

Thanks for the update. Please reply here if you have any further questions.