Even after upgrading to 15.6 the lens metadata is not showing in the library module
If this is occurring with photos that you imported into your catalog using LR CC 2015.5, then see this help article for how to correct the problem: Lens metadata hidden for some cameras in Lightroom 2015.5 and 6.5..
If this problem is occurring with photos newly imported with 2015.6, then the most efficient way to troubleshoot that is to upload a problem photo to Dropbox or similar and post the link here. We can then see what's going on in detail.
Retrieving data ...