Screen glitch when two users are logged on

Solution 1:

Start with:

1. Reset NVRAM / PRAM
2. Reset the SMC

If your Mac has a double GPU:

3. Disable the Automatic graphics switching located under System Preferences -> Energy Saver.

Disabling this option will force the Mac to run with the dedicated GPU. From the issue described above it seems a bug in OS X that enable both user profiles to have control over the GPU, even if one is currently inactive.

If this does not solve the issue:

4. Boot in safe mode

   • If the problem persists also there it could be caused by an installed software. At that point you can proceed by exclusion.