Originally Posted by an0ther
Did you boot system after unlocking boot loader? or did you flash twrp right away. also 22.214.171.124 is out. Did you use the UL_CA twrp and not the WHL? Need more info, has it booted since you installed twrp?
Yes, I remember booting back into the phone after unlocking the boot loader. I made some calls, sent some texts, then flashed twrp.
I used the UL-CA version after following these instructions. androidcentral.us/2014/04/root-att-htc-one-m8/ (ugh, won't let me link)
I'm not sure what the difference between that and the WHL is.
Also, not sure what you mean by "has it booted since you installed twrp", I've tried rebooting it numerous times, but it just goes back into twrp.