I started having this issue annd was completely lost to the cause. I saw suggestions to change Monitor Profiles, Disable graphic accelartion etc.
It turns out, for whatever reason, it was all do to video card settings, with-in my video card (Radeon) driver software settings. Software usees "profiles" so I can't say what setting changed, I just disabled everything by setting it to standard, it basically made my image look "unedited" in Develop, but the images matched again, mostly, in Library and Develop.
Just wanted to drop a note if anyone else is having this issue.