Welcome to our community.
This is a known issue and our team is looking into it. We had a few reports about it in our performance feedback thread here:
Our community has found a temporary workaround for this issue, that is either upgrading the internal hard drive of the PS4 Pro to a SSD drive, or installing the game on an external USB SSD drive.
While this is not an ideal situation, it could be useful while our team is working on this problem.
Thanks for your feedback.