Several weeks ago, my Lightroom 6.7 (standalone) started to exhibit the following behavior on startup. In the Library module, with Loupe view mode set, an image appears (the one from the previous session). If I change the image selection in the filmstrip (mouse or cursor), the Loupe view image does not change. If I then exit Lightroom and restart it, the behavior reverts to normal. Changing the filmstrip selection displays that image in the Loupe view. Exiting at this point and restarting, will usually be fine. So far the behavior is random, I've yet to discover the sequence to get the failure.
One thing that I do know is that I just purchased a years subscription to Lightroom/Photoshop CC. The exact same problem exhibited itself on the very first startup!
For some reason, I am feeling like the errant behavior started around the time that I received an update to 6.7 (standalone).