This message was posted on behalf of Intel Corporation
I understand that you are having a refresh rate drop when you are playing games at full screen, I apologize for any inconvenience.
Regarding this, I was checking and this unit supports 3840x2160 @60Hz only while using display port. When using an HDMI the max. resolution is 2560x1600@60Hz. This means that the refresh rate drop is happening there.
If possible, I would recommend you to use display port. If not then it needs to be a lower resolution if you want higher refresh rate. Also, if this does not solve your question, To better assist you with your request, I will need to check some information about your computer. Please follow these steps:
1. In the keyboard, press WinLogo key + R.
2. In the Run box please type dxdiag and hit Enter.
3. Click on Save All Information (save it in your desktop).
4. Attach the report to this thread.