I know this is the SME forum, but a long shot someone might know what is causing this. Have a request open with Apple, so far nothing.
Having some weirdness with a local charity and SMB shares from SME 9.1
Customer foolishly upgraded to MacOS Sierra.
None of the mapped shares work, neither are they able to browse the servers shares directly with cifs://servername
Up pops a dialogue with "Too many connections, the server may be busy, try later!"
Of course everything else on their network works fine with SME, Windows and Linux workstations.