Samsung Galaxy S6 screen rotation Bug work around
After discovering my gallery app would no longer rotate into landscape but all other applications did, I tried a workaround that seems to work fine.
The conflict seems to happen when using a different laucher then charging the phone. Switching back to the default launcher has no effect nor does clearing cache in the Gallery app etc.
If you revert to the TW launcher use rotation lock, clear backgrounding apps and Ram. It appears to resolve the issue, even when disabling the rotation app. If you return to another launcher the problem re appears and you will need the rotation lock app set to forced Auto.