Could you please let me know the version of Lightroom installed on the computer.
Also which operating system are you working on, MAC or Windows ?
And does it happen with all the Collections in the Catalog.
I am using OS X El Capitan and Lightroom CC 2015.2.1.
It only happens with one Collection.
You should update LR to 2015.3.
When I try to update Lightroom, it tells me that I have to close Lightroom before I can update it. How can I update Lightroom without opening it to select Lightroom?
Open the Creative Cloud desktop app and update from that.