If you scan a remote directory for a list of files by using opendir and readdir on a path obtained from ssh2_sftp(), you'll end up with a list of full file paths containing the ssh2.sftp://$sftp prefix, where $sftp is the sftp resource string returned by ssh2_sftp.
If you later attempt to use ssh2_scp_recv() (even on the same connection!) to copy files locally from the remote path, the copy operation will fail because ssh2_scp_recv() doesn't like the wrapper path prefix. It expects remote file references to be rooted at the base of the remote file system (eg., '/').
Moral: ssh2_scp_recv() likes paths rooted at the file system root on the remote machine, not full network paths. This routine will fail with an obscure message about not being able to copy the files - yet when you go look it works fine. Worse, when you connect and copy them from an scp shell session, it also works fine.