Sorry for this problem. can you please mention your Premiere Pro version and system details? Please try the same in the latest beta build also. You can download the latest Premiere Pro Beta build from Creative Cloud --> Beta apps --> Premiere Pro (Beta)
Please try and let us know how it goes in the beta build. If you still see this issue in beta builds, please share your original footage/project & export settings. We will check it at our end and take quick action.