This is by far the worst release of Premiere Adobe has ever put out. It's riddled with bugs... Having very similar issues and exports are even looking different than how they are in the program.
Mod note: This post is OT and the title was changed to reflect your issue. Thanks.
Sorry about that. Are you using HDR footage - Sony or Canon gear? It sounds like you are hitting the same issue many others are. It's not a bug, there is more of a new workflow you must abide by. If you are unaware of this change, and you do not have the hardware to monitor HDR footage - it might be better to roll back to the previous version. Let me know if you have questions.