Finally i installed the TWRP and now i have same problem as you have.
Every time i reboot my phone TWRP disappears
Do you found any way to solve this problem?
Thanks
Edit:
this post on reddit helped me
Step by step guide: (Rooting the Moto Z (XT1650-05) on stock 7.1.1 NPL26.118-20)
1 - adb reboot bootloader
2 - fastboot flash recovery twrp-griffin.img (I used this:
https://www.androidfilehost.com/?w=files&flid=157130)
3 - You probably see corrupted message. ignore that
4 - DON'T fastboot reboot bootloader, if you reboot the recovery will disappear.
5 - Use volume keys to enter the recovery, wait few minutes to TWRP opens.
6 - Download lasted magisk and flash via TWRP (Here:
https://xdaforums.com/apps/magisk/official-magisk-v7-universal-systemless-t3473445)
7 - Done. the TWRP will remain after every reboot.