Trouble with disable switching time zone

Just found a kid's phone which has all the screen control and content restrictions, one can change the time zone. Location services is on, set time zone greyed out under system services.

After many tests, found out disabling set time zone under system services actually turned off location service (even though the location service is still on). From general -> Date & Time, I can see "Automatic time zone accuracy is improved when location Service is turned on" which is usually shown when location service is off.

Anyone knows how to fix it.