Before having the Lollipop upgrade and you have rooted already, but lost it because you accepted that, you do not need to manually root your device.
So, regain freedom by following this tutorial to simply re-root your device. This should be less hassle because it is as easy as elementary.
1. This is for HTC One (M7) devices only, running Android 5.0+ Lollipop firmware.
2. Recharge before starting. This is to avoid unexpected interruption that could cause brick.
3. Do a data back up just in case. But still, this will not wipe anything.
4. Do this at your own risk.
Pretty sure, you know how to enable USB debugging if you have done flashing yourself. But in case you forgot, read this.
Connect to PC. Now go to get the latest HTC drivers. Download and extract the HTC One file. Open the program Device Manager > Other devices > My HTC. Right click and update driver software. Then, browse and select the file you extracted. Continue until successfully updated.
And, this time, fasboot reboot-bootloader.
Once booted, enter Recovery Mode which is now TWRP. Flash the updated SuperSU unextracted zip file that you should have put in your internal storage.
Wait for it to finish and so restart the system using one of TWRP’s option. Download Root Checker app, and verify if you have root access. Launch it and SuperSU will ask to write binaries so just grant, except for the Knox notification. You can now see that the Root Checker app verifies and confirm access.
There you have it! You have successfully re-rooted your HTC One finally, even without having to perspire. Enjoy its benefits!
For a video see: