Adobe has acknowledged the issue in this bug report: Lightroom: Lens metadata field missing on import | Photoshop Family Customer Community. So far, it's only been observed with Nikon NEF files. Please add your vote and details (including camera make and model) to that topic, to make it more likely Adobe will prioritize a fix and to get updates on the issue.
Yes, Nikon NEF files, copied as DNG's.
I just ran into this problem also (using a Nikon D750 and running LR 2015.5 on Win 7 x64).
Serious problem for me - and it also breaks any smart collections that rely on lens name metadata as newly imported photos aren't being indexed with the lens make. Even worse, exported files also don't include the lens make... I'm just rolling back to 2015.4 now...
Edit: rolled back to 2015.4. I then had to remove the newly imported photos from my catalogue and re-import them - and presto, up popped all the lens metadata. Fingers crossed for a fix (in several months time no doubt) with 2015.6 / 6.6.
Having same issue. Lens used not shown in LR EXIF data nor in overlay. The profile does show up in the Develop module in Lens Corrections however. Spent an hour chatting with support who couldn't fix the issue for me tried and failed to roll back the version of camera raw. Never got a straight answer from support if this was a known issue, sounds like it is. This all started when I update about both LR and PS 19 days ago (issue occurs in both). Older shoots with same camera and lenses (Nikon D800E 24-70mm f2.8 & 70-200 f2.8) do display the info. When review EXIF info using a non-adobe app the lens info is there. While not the biggest software issue I've dealt with it is a annoying. From time to time I sort based on lens used. Now all pics get dropped into an "lens unidentified" bucket.