[OnePlus 6T  Questions & Answers] Jhawk2k18:
No worries!

Hello, I am sorry to hear of you having this issue, I just went through 3 1/2 days (off and on) of recovering my T-Mobile OnePlus 6t which I found a way to get my unlock code within 2 weeks of having it, so I rooted it and put a custom kernel on it, stuck on 9.0 never let me update as I was not familiar with A/B partitioning, yet! The answers I saw to your questions were spot on, I just had a little to add to it and I'm sure I am not alone. Real quick let me list what has gone wrong on the rare occasion it hit the fan with the 6t...

- When I would accidentally and rarely let my battery die it seemed like it took forever to get it to reboot, I mean it sat on my desk of DOA devices for 2 weeks!

- It often seems like the buttons do not always respond properly and never have when I needed them to. Been through this before, I've bricked and unbricked and flashed and re-flashed and wiped all weekend and I like Android 10 and all but seems everything is different for every build, and everything seems to have to go in the right order with the exact right file or you wind up in a jam, period..

- That said, the previous person that answered your question has likely encountered similar, I've heard of right down to the buttons not physically working, but I have been a Smart Device Master III Technician for over 5 years, i know my buttons were not broken.

- Most likely culprit that I just handled and worked, i did have to use the MSM tool, several times - and re-unlock the BL, several times I would not even get the chance to get to fastboot, just a screen saying Build and Hardware not a match"" in yellow letters and it just bootlooped. No fastboot is no good, but when you said the tool would show some signs of working but then not, I have 2 solutions that I needed on diffrent occcasions.

1 - As mentioned fully try other USB cables, and ports, if you pull the usb-c out of the port and hold <power + vol up + vol down> eventually it will do something, very picky, sometimes gotta move your fingers to different spots on the buttons and also after 15-20sec let go of power and hit and hold it again... after a few seconds before it vibrates stick the cable in connected to your PC and the screen will be black (obv) but the msm tool will pick up on it. I know about the cables because I take good care of my phones and cables and charging ports, however on my final fix today it showed in msm tool it was connected but waiting for device.... Fed up i put the phone down and moved the usb cable a little bit and it picked up on it and did its thing! That part was just the cable, getting into qualcomm mode or w.e. is a bit tricky sometimes.

- Also someone said set it down for a while and come back to it.. THAT WORKS!! Let it fully charge and often just plugging in charger turns it on, bootloop soft brick or however have you, very simiilar to an Apple device and their DFU (don't f up mode cause screen is black..)

I hope that helps you get in touch with your family and friends.. Whatever you do, don't give up bc if you have not got it yet, you will! One other note, there are a few different msm tools available and they look the same some same size, but the one that supposed to work on my phone didn't and one that they say only a fool would attempt to try actually saved me, so if all else fails, use a different msm tool/usb cable and you will get it! I don't think I can post links yet I am on here very rarely, but plan on more! I have received so much help from XDA throughout the years on thousands of phones with just software issues alone, aas well as guides to my own phones. I would be honored to give back as I also have some extensive knowledge on many devices but I am a noob in comparison to many! Stay safe, good luck and please update and let us/ me know how it worked out for you. If i can help further I will, I have every firmware file for the OP6t, recovery, tools, software, this is not new to me but I feel your frustration!