Please try and reset the Lightroom Preferences to default Or create a new catalog
Let us know if that helps.
I have reset preferences twice and reinstalled twice. It happens on every catalog new or upgraded from earlier versions of LR.
A number of people have reported this bug in the official Adobe feedback forum: Lightroom CC 2015.1.1: Develop module doesn't detect external changes to original file. Adobe Chief Customer Advocate Jeffery Tranberry said, "Our QE have a repro case and the engineering team is investigating this issue." Please add your vote and details about your issue to that bug report. Just because Adobe has acknowledged a bug doesn't mean they will necessarily prioritize the resources to fix it in the next release, so the more people report it, the more likely it will get fixed sooner. Also, by adding your opinion and following the topic, you'll get notified of any changes in status.
Meanwhile, revert back to the last stable release, CC 2015.1.1: How do I roll back to Lightroom 2015.1.1 or Lightroom 6.1.1? CC 2015.3 is rumored to be coming out soon, but be patient for a few weeks and let others do its beta testing before updating, while you're getting productive work done.