are u using stock rom with root?
if so then the reboot option will always only reboot the phone, not reboot to recovery of choice.
try third party app that has option to reboot to recovery like Goo Manager
Evolution of my Android:-
Sammy SII < Note N7K < Note II < SIV < Note N9K5 < LG D802
Cloudy Stock 1.3 with twrp 2.7 enhanced with SimpleKernel v4