It have been about 2 years, I finally get a U11 plus to make TWRP device tree with working decrypt function.
Please download latest TWRP build in following link.
PS. watch out the last 6 digits at the filename, it must equal to your system's android patch level. e.g. 2017-12-01 (Dec, 2017) = 171201, otherwise TWRP will not decrypt data partition.
PS2. U11+ already get Android Pie update, but this update will break data decrypt function in TWRP recovery.
@nkk71, thanks all the works you've done for us.