I did some more searching, but could only find some postings regarding ‘empty directory’ using SMB from an iPad, but no solutions.
The Synology NAS has no issues, so is there is difference in the SMB configuration of Asustore ?
Is AFP filesharing enabled on the Asustor ? I have it disabled since it is an obsolete protocol.
There is also a ‘fruit’ VFS module in Samba to improve/fix issues with Apple’s SMB3 implementation and seems to be incompatible with Netatalk AFP :
https://groups.google.com/g/linux.samba/c/qEw8TS1rG-E
I saw references to this ‘fruit’ module as fixes for read-only files on SMB shares from macOS.