Answered
When I merge layers I have this issue


This just serves to verify @Stephen Marsh ’s suspicion:
Does turning off »Use Graphics Processor« in the Performance Preferences (Photoshop > Preferences > Performance > Graphic Processor Settings) and restarting Photoshop have any bearing on the issue?
If it makes a difference then procedd according to his advice.
Already have an account? Login
Enter your E-mail address. We'll send you an e-mail with instructions to reset your password.