[OnePlus 6T  Questions & Answers] flash713:
How did you try a rom with a locked bootloader? You have. A 6 or 6t?

If you cannot get msm tool to work unfortunately you're out of luck unless you take it to a service center and from what I've seen on here the cost isn't worth it. Better to get another device.. There are two threads for this crash dump, this one and another in oneplus 6 forums. I probably got confused and that's why I commented what I did. Windows is ****. I can't stand it and don't use it ever, except when it's absolutely mandatory because whatever I'm using requires it, which is extremely rare. The only thing you can do at this point unless you have already done it is read the entire thread a few times on msm tool and if you can't get it to work then sell it as is or take it to a service center. Most of the time, not always but most of the time msm tool will work. Unless you already have,, If I were you in same situation I'd try the patched msm tool, the one for converting from T-Mobile to international model, and I would also try and run the T-Mobile msm tool 40 exe or whatever it is. Not saying you you have but I've been on xda since Nexus S days modding my phone's and tablets and there are times I look over something simple and realize later and go back to it and end up getting it to work. I hope you get it going.

When you plug in your device , powered off , holding volume keys down with qualcomm usb drivers installed what does it say in device manager???

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From here down is not directed at anyone particular just some tips for anyone with a locked bootloader and a 6 or a 6t. From what I've read crash dump mode happening is kernel related and there are different reasons why a device goes to crash dump mode.

One of the riskiest moves anyone can ever make is locking their bootloader. I say this because I've seen many people ruin their phones that way over the years here on xda. I think maybe many people don't understand about the whole bootloader unlock, lock.. All it means if a bootloader is unlocked is it's a sign to whoever has the phone that it's been altered. Besides that idk of any other security issues having an unlocked bootloader may cause. I keep mine all and always have kept bootloader's unlocked and dev options and usb debugging checked.

Seems like this is a thing for oneplus 6 and 6t for some people. I've seen crash dump on my oneplus 6t ten or eleven times,, maybe more and a few of the times it showed different reasons below where it reads the "crash dump." Last time it showed "fatal error ..... " I manually booted twrp, flashed OOS and a rom formatted data and it booted fine but that time it would not come out of crash dump like all times previous. It would loop around when I attempted to reboot system using button presses but luckily I had bootloader unlocked, dev options and usb debugging on so I was able to fastboot boot twrp and then flash something and it worked.

**If anyone reads this and has a locked bootloader and or doesn't keep dev options and usb debugging enabled I would definitely unlock it and keep it unlocked and make sure you always enable developer options and usb debugging as soon as you install and reboot system. Seeing how this seems to fatally kill people's devices in some situations where what I say here is not done. Anyone using a 6 or 6t without an unlocked bootloader and dev options and usb debugging not enabled is asking for it. You can always delete lockscreen. Directions on how to delete lockscreen are on the how to root thread in guides section by FunkWizard.