Being logged in over ssh while initiating a Firmware Upgrade results in a bricked device.

[lancethepants]

I have an RT-AX88U and I've noticed if I have an ssh session open while flashing a new firmware to the device it results in a bad flash every time, requiring a recovery using the Asus Firmware Restoration tool. I've tried with both dropbear and openssh. I can even close the ssh session immediately after beginning the upload of the new firmware but it will still brick the router.
I wonder if it has an issue unmounting file systems when upgrading?
The reason for using ssh was with local port forwarding to get access to the web ui from outside the network for upgrading the firmware. Just wondering if others have experienced this and also, what's the best way to remote update the firmware, vpn? I don't suppose there's a cli way to update either?

 

[RMerlin]

That makes no sense to me, as the majority of the time I flash a new test image, I am currently logged over SSH at the same time, without any issue.