[HTC U11  Questions & Answers] Matty1993:
Hey mate can i ask did you boot the rom before locking the bootloader to see if the OS was functional ? Also how many times did you try flash the updated RUU before locking the bootloader,

Youve locked the bootloader down again anyway and will display as relocked in bootloader mode, youve made things a bit harder for yourself here,

Never ever relock the bootloader whilst the system is non functional keep it unlocked until you know the OS is ok, in general now youve locked it your device would usually require a very specific RUU full signed and exact main version match, however luckily for you if you havent already fixed it ive found a way to fix it without sending to HTC if you dont have the exact RUU needed to revive it,

What i want you to do is download the full RUU.zips for your model from the google spread sheet main version wont be an issue will be best to get all releveant RUUs with matching CID from there also

https://docs.google.com/spreadsheets/d/15JL3tRWDSVOUKo_revEYtQ_tRcOSJ0vWcvk8a7TK8Hk/edit?usp=sharing

Now download the HTC_10 batch tool and install it

http://xdaforums.com/showpost.php?p=67056758&postcount=4

After its installed, place your RUU.zip into your local drive "C://" as an example where your batch tool is installed place the RUUs 1 at a time into /android/com, no more than 1 at a time when flashing

Full length of where RUU needs to be put in simple termns is C://android/com

Now minimise to the desktop, then right click on the batch tool icon and run as administrator,

NOT the HTC FUU icon !

Once the batch tool has booted, press the number 3 on the keyboard and then enter, this will take you to the fastboot terminal,

Take note the screen should be purple and the location on the screen should be as follows C:// is only for example your drive letter may be different,

C://Android/com

Now boot the phone to download mode and connect to pc,

Now type the following,

Fastboot devices

If that didnt work type

htc_fastboot devices

Your device should display now with a serial number,

Now type

fastboot oem rebootRUU

If that didnt work type

htc_fastboot oem rebootRUU

Now type

fastboot flash zip example.zip

If that didnt work type

htc_fastboot flash zip example.zip

!!example is the name of your RUU if you dont want to type it out drag and drop from the minimised window in C://Android/com,

Now your device will start flashing the RUU to your device, in my experience this is the only fastboot terminal that will revive a dead htc in your case without the exact signed ruu it requires,

It will also let you rollback from oreo to nougat whereas any other fastboot terminal you use will give you RUU error Main version fail in info or RUU error zip from usb command,

Try this it will work if you need clearer instructions you can check my thread out, this is pretty much the same case but without the device saying corrupt either way you still have non functional OS and oem unlock will be off FRP lock will be enabled and you wont be able to unlock the bootlaoder again without a functional OS as the full RUUs wipe the device completely resseting everything

My thread link is here for more infomation if needed

https://xdaforums.com/u11/help/fixed-htc-u11corruptrelockeds-t3855157

Thanks