Irritating SanDisk Cruzer 64GB thumb drive quirk

Slim possibility: there may be another wrinkle or two here - and that would be the format of the files. For instance, if you burnt a video to a DVD, you need software to render/format that file so it will play on a stand alone player. The result is great, but if you wanted to burn that again, you would first need to transfer the video back to your computer and need an encoder to change the format again. In other words, depending on their format, you cannot drag and drop some movies or videos from a computer to a hard drive and/or back again - it may not play correctly. And, the other possibility may be that you are running into DRM and/or copyright issues which some companies have started using.

Which format did you use? ExFat? I don't own a BR drive but I'd imagine they use only certain formats. Sounds like you have compatibility problem.

I do have several Sandisk 64GB Cruzers like yours. I would never use them for what you're wanting to do as they are all dismally slow.

For transfers like you're doing I use a 500 GB Samsung T7 portable SSD.

If the check the Blu-Ray player specs. It may only support FAT32 file system or maybe NTFS. If it is only FAT32, there is nothing you can doo as it has a fixed 4G limit. If it accepts NTFS, which does not have the 4GB limit, then you need special software on the Mac as macOS cannot write to an NTFS formatted disk.

It's just a potable USB drive with both A and C cables. So far it's worked everywhere I wanted it to on both Windows and Mac. It can be formatted as needed. I have no idea about BR drive compatibility, but if other USB drives work on a BR drive I'd think it would too once in the appropriate format.