My apologies. When I post, I usually try it all and assume people know I've done it.
3CX Version 16.0.2.910
GrandStream GXP-2135, fw 1.0.9.132
3CX Template.
I can't say because I assumed it worked (lab system), until one of my guys who tries it all noticed it. We factory reset the phone , and same behavior happens.
Backlight timeout setup at 1min, Screensaver setup at 3min