I just installed the Update 9.0.2 for the Onplus 6
Usually I shut my mobile off during night and charge it.
The usual bahavior of the mobile is
switching on to charge mode ->
Bootloader unlocked warning ->
afterwards animation of charging the battery.
With the new firmware it stays at the Bootloader unlocked warning screen.
I checked already Magisk Versions 17.1, 17.2, 17.3.
Magisk Uninstall / reverse to stock boot image solved the behavior.
Dalvik Cache were cleaned.
Complete reset / format of all partition didn't solved it.
I think there is a bug with the magisk patched boot image that is causing the not switching inzo charge only mode.
Previous firmwares for Oneplus 6 had no issues with charging while being off.
Update: its an issue of the Stock Rom from oneplus.
9.0.2 freezing at bootloader warning
9.0.3 charge like expected
9.0.4 freezing at bootloader warning