I tried to run 9 1070's a few days ago on a Z270A-prime. Windows detected all 9, but claymore 9.8 would lockup on startup. My windows update is probably a month old though, may try the newest update today.
I wonder what windows update gives the ability to run more than 8 video cards per driver.
Maybe this is the fix, it is the only thing i found on 1703.
Addressed issue where device drivers are not loading.
https://support.microsoft.com/en-us/help/4032188