According to your description, the old external hard drive mounts on the 2008 MacBook, and all files and folders are visible there, it indicates the old external hard drive is intact, there could be some issues with the connection between the drive and your Mac or with the macOS.
Hence, you can isolate the issue that the files on the old external hard drive not showing up on the 2017 MacBook by checking the connection, if you used the same USB cable or hub to connect the drive to both Macs, try to connect to another USB port on the 2017 MacBook.
Besides, you can try to restart the Mac, update the disk driver, update macOS, and reinstall macOS to eliminate the OS-related issues. Then, reconnect the old drive again to check whether the files are visible now.
