Pro Tools 12.6.1
Mac OS 10.12.1
It seems Pro Tools 12 has issues with reading some metadata. This problem may have existed in 11, but I upgraded straight from 10 to 12, so I wouldn't know.
I discovered a few of my sound effects libraries were having trouble importing files from the workspace. They are stereo files, but I was only able to drag them to a mono track. Also, once putting them on the mono track, the clip would be offline, and the window to automatically or manually relink the files would pop up. Lastly, I noticed that the offline clip always had ".A2" added to the end of the name.
I narrowed it down to the fact that the files that I was having trouble importing all had the value of "(A1), (A2)" in the Channel Names column of the workspace. Other files (even from other libraries created by the same company)that did not have this seemed to work fine. Once I removed this metadata from the files, they also worked fine.
My first go around with this, I thought that it must have been just the one company's files, as only a couple of their libraries had it and thought the problem was solved. But I am now finding other libraries from other companies with the same issues. Which makes me think that this might be a relatively common type of metadata to have, and Pro Tools must have a bug in reading metadata from this column?