Through Sin[x]^6 + Cos[x]^6 // TrigReduce operation, we can know that the minimum positive period of Sin[x]^6 + Cos[x]^6 is Pi/2
But
Periodic`PeriodicFunctionPeriod[Sin[x]^6 + Cos[x]^6, x]
returns Pi.Refer to this link.
How can MMA solve the minimum positive period of a function by a common method?
FunctionPeriodit says :gives a periodand notminimumperiod. So $\pi$ is valid period. Also comment there by JM in the link you posted saysAnother possible weakness of the function is that it does not always return the minimal periodso may be one should callTrigReducefirst and then callFunctionPeriodon the result. Then it does returnPi/2in this case. May be WRI should fix this function so it returns minimum period. – Nasser Jan 20 '20 at 07:15