Error when copying files from Files app on iPad (or iPhone) to samba share

As per this earlier question (unanswered),: Error when copying files from Files app o… - Apple Community

I have a puzzling issue with copying files from my iPad and iPhone to my shared truenascore drive.

Both are at i(Pad)OS 17.5.1 and I can read from the drive with no problems. I can also write from my Windows 11 dell. Writing also works from my wife’s Macbook and (even more bizarrely) from her iOS 17.5.1 iPhone using my truenas ID; it also works fine from my son’s android phone.

The Files App is clearly lying when it says “The Operation Can’t Be Completed: You cant copy the item xxx.yyy because its name is too long or includes characters that are invalid on the destination volume”. This fails consistently (for me) across both devices and using various test files. Interestingly, after the bailout, it leaves a zero-size file on the target drive with the correct name, suggesting that the FAT entry (if they still call it that?) is OK, but the file itself is not written.

Having tested other devices and stacks, including a superficially identical device (my wife’s phone), I am basically out of diagnostic ideas. Any suggestions (apart from “don’t use the Files app”) welcome.

Thanks