Playing a video in MX Player Pro turns the phone's brightness to extremes. What is the cause?

Used MX Player Pro for years on my S6, S8 but on my new Note 9 every time I try to play a video the brightness of the whole phone screen goes to extreme brightness that I have to turn the phone fully away to close the app. What is the cause & fix? Note 9 is a year old phone so I thought any issues would be fixed by now.