Let's try to reproduce what FFS does by using Windows Explorer:
1. On the *local* drive rename "ami.pdf" to "ami.pdf.ffs_tmp"
2. Copy "ami.pdf.ffs_tmp" to the MTP device using Windows Explorer
3. On the device, rename "ami.pdf.ffs_tmp" to "ami.pdf" and see if this fails.
If this is still working, then maybe there is something for FFS to fix an we can dig deeper.
I encountered this error when I synchronized folders between my desktop and smartphone on Android 13. The problem disappeared when I unchecked "Fail-safe file copy" in the settings.