iPad can't activate Dolby Vision

iPad Pro (12.9-inch) (6th generation)
iphone xs max
iPad will load Dolby Vision video twice, but it will only load once on iPhone.
The color played by the Dolby Vision video on the iPad is correct, but the brightness is very dim.
infuse pro 7.8.1(4924)the same situation in infuse pro 8.0(4927)