I also have this problem, with slightly different symptoms from the posts above that I have read:
On using SU after a fresh boot all is fine for, often, some hours. Then suddenly the Select tool (and much else in SU, such as menu navigation) goes v v v slow.
The problem is sometimes cured by one of:
- log out and log in
- exit SU and leave it for 10 minutes before restarting
The problem seemed to start after Windows 10 "Creators update".
I am running Windows 10.0.15063.413 (ReleaseId: 1703)
I have integrated Intel HD (Driver Version: 126.96.36.19959)
If I have the energy I will try a full SU uninstall/reinstall.