/authorize is slow

Our site loads quite slow after successful login.
We noticed that Auth0: Secure access for everyone. But not just anyone. is not stable. Fastest time to load is 260ms but in average we are over 750ms in our production tenant. On the other hand our development tenant is stable on 260ms.
Additionally, we always have to call get access token afterwards which takes also ~300ms.
What should we do in order to make sure both are stable