I can provide you all the logs you want.
I already looked at the logs on the NAS, I do not see anything concluant about that.
On the Linux boxes I have stuff like that in the logs (dmesg) :
CIFS VFS: No response for cmd 162 mid 59915
CIFS VFS: No response for cmd 4 mid 59914
CIFS VFS: Send error in Close = -11
CIFS VFS: No response to cmd 46 mid 59912
CIFS VFS: Send error in read = -11
CIFS VFS: No response for cmd 50 mid 59913
CIFS VFS: No response for cmd 50 mid 59911
CIFS VFS: No response for cmd 50 mid 59910
CIFS VFS: No response for cmd 50 mid 59909
CIFS VFS: No response for cmd 50 mid 59907
CIFS VFS: No response for cmd 50 mid 59906
CIFS VFS: No response for cmd 50 mid 59905
CIFS VFS: No response for cmd 50 mid 59904
CIFS VFS: No response to cmd 46 mid 59908
CIFS VFS: Send error in read = -11
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: No response to cmd 46 mid 59037
CIFS VFS: Send error in read = -11
CIFS VFS: No response for cmd 47 mid 59032
CIFS VFS: No response for cmd 47 mid 59031
CIFS VFS: No response for cmd 50 mid 59036
CIFS VFS: No response for cmd 50 mid 59035
CIFS VFS: No response for cmd 50 mid 59034
CIFS VFS: No response for cmd 47 mid 59033
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: No response for cmd 50 mid 63899
CIFS VFS: No response to cmd 46 mid 63891
CIFS VFS: Send error in read = -11
CIFS VFS: No response for cmd 50 mid 63898
CIFS VFS: No response for cmd 50 mid 63897
CIFS VFS: No response for cmd 50 mid 63895
CIFS VFS: No response for cmd 50 mid 63894
CIFS VFS: No response for cmd 50 mid 63893
CIFS VFS: No response for cmd 50 mid 63892
CIFS VFS: No response for cmd 50 mid 63890
CIFS VFS: No response for cmd 50 mid 63896
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in read = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9
CIFS VFS: Send error in Close = -9