When I click on the exclamation mark, sometimes I get the following message: "The metadata for these one or more of these photos has been changed by both Lightroom and another application. Should Lightroom import settings from disk or overwrite disk settings with those from the catalog? And the options given are:
Import Settings from Disk
I am never sure what impact these commands would have on the image file data. Obviously these images typically have been edited with the OnOne or Nik plug-ins and I wouldn't want to loose the final edits.