hi ,

i am trying to group by date field which is lookup column not grouping properly 

Bug : if date value  is less then 12 group by interchanging date and month field in group by view

example: 06/11/2015 

06 date

11 month

specifically if column is Lookup column

Hi,

Please install the latest cumulative update for SharePoint 2013.

July 14, 2015, cumulative update for SharePoint Server 2013 (KB3054937)

https://support.microsoft.com/en-us/kb/3054937

Or as a workaround, we can create a calculated column and group by this column.

Best Regards,

Dennis