Core recovery files for the Team Win Recovery Project (T.W.R.P) - this is not up to date, please see https://github.com/TeamWin/android_bootable_recovery/
Its Because The firmware V30 or V27 Doesn't supports Reboot to recovery in miui (Or many other ROMs) its fixed in latest nougat and oreo ROMs By team ghost
Xiaomi Redmi 4X flashed 3.2.1-0 by fastboot mode. Currently am on 8.1.4 xiaomi.eu rom. But I had this issue with previews TWRP version also.
While in TWRP Recovery Project, if I select [Reboot] to [Recovery] does not reboot to recovery, never. Always reboots to System automatically.