Happened to me as well but it lasted about 5-6 seconds. I was already within Haze ult and then a Wraith ult lifted me up at which point lead to the frame freeze.
1. Reload ur PC
2. If nVidia go to C:\Users\UR_USERNAME\AppData\LocalLow\NVIDIA\PerDriverVersion\DXCache
If AMD go to C:\Users\UR_USERNAME\AppData\Local\AMD\DxCache
3. Delete all files in folder
4. Go to Sandbox and activate Haze ult to cash the effect
5. No FPS drop more
1. Reload ur PC
2. If nVidia go to C:\Users\UR_USERNAME\AppData\LocalLow\NVIDIA\PerDriverVersion\DXCache
If AMD go to C:\Users\UR_USERNAME\AppData\Local\AMD\DxCache
3. Delete all files in folder
4. Go to Sandbox and activate Haze ult to cash the effect
5. No FPS drop more