That's a but with some Macs that's been reported previously.
What system and Photos versions are you running? If you're not on 10.15.5 download and apply the macOS Catalina 10.15.5 Combo Update.
Try the following:
As a test launch Photos with the Option key held down and create a new, test library. Import some photos and test to see if the same problem persists. Does it? (This tells us if the problem is limited to your current library or is more wide spread)
Next log into another admin user account, Set up users, guests, and groups on Mac, and see if the problem persists. (This tells us if the problem is limited to your user account or is system wide).
Also be sure to r report the problem in detail to Apple via Feedback - Photos - Apple