Error nfs_isdir

That item is a folder

A file operation was attempted on a folder. Refresh — the item may have changed type on the server since it was listed.

What this means

NFS status 21, EISDIR. The name refers to a folder, and the operation (download, overwrite, delete-as-file) only works on files.

Usually

The listing was stale: a file was deleted and a folder created with the same name, or a symbolic link now points at a folder. Pull to refresh and try again. If it persists for one specific item, look at it on the server itself.