The emulator now freezes.

I usually use the SDK emulator that comes with Android Studio.
The main Nexus 5 emulator now freezes.
Specifications are as follows:

• Model: Nexus 5
• OS:Android 5.1.1 x86
• Emulated Preformance:Use Host GPU
• RAM:1536MB
• VM heap: 64 MB
• Internal Storage: 200MB
• SD card: Studio-managed 100MB

This emulator includes apps under development and testing.
I think it started to freeze a few days ago after I tried GPU overdrawing and shut down the emulator, and there are three main times when it freezes:

• Lock Screen
• After Unlocking
• Operating the app

Recently, I feel that the time to freeze has been extended.
I tried turning GPU overdraw on and off again, but it didn't seem to work.

When I tried to run the test during the freeze, I got an error message asking if I forgot to start Activity for tests that were not UI-related and UI-related:

android.support.test.espresso.NoActivityResumedException: No activities in stage RESUMED. Did you force to launch the activity.(test.getActivity() or similar)?
at dalvik.system.VMStack.getThreadStackTrace (Native Method)
hereinafter abbreviated

I don't know how to run tests that are not UI related, but
It may not be completely frozen.

Currently, I try to use something else instead, but
If anyone knows why this emulator freezes, please let me know.