samba - Feb 2017 - timeout after inactivity on mount.cifs

Hi,

I'm trying to backup a directory on a Windows 2008 (fully updated)
I'm running Debian testing.
(kernel version: 4.9.6-3, mount.cifs version: 6.6)

I'm basically mounting a share with mount -t cifs and tar the content of 
a directory.

I didn't have problems with old debian (probably sqeeze).

Now I occasionally get in dmesg:

cifs vfs: error -32 sending data on socket to server

and tar says
tar: /sharepath/: Cannot stat: Host is down
but then continue to archive the share

Sometime cd into the mounted path takes several seconds.

I've a script that every minute does

smbclient -A"$CREDENTIALS/credentials" -L IP > /dev/null
2>&1

to check if something is wrong with the Windows server or connectivity 
but after several days running it, it hasn't failed.

It seems that mounting the share and immediately starting tar reduces 
the chances to run into problems.

It looks like a timeout problem.

Is there anything I can check to circumscribe the problem or even better 
solve it or does it look like a bug?

thanks

-- 
Ivan Sergio Borgonovo
http://www.webthatworks.it http://www.borgonovo.net