Ive got an iPad mini 4 in a Wall Smart in wall mount (although this issue will presumably relate to all iPad docks, iPort etc..as it seems to be with the iPad / iOS rather than any dock).
Ive installed a few of these in the past couple of years and always set the sleep settings to "never" and then put the iPad in guided access mode to using this technique
"lock it" to the control system app. The wall dock is powered so the iPad just keeps running.
Recently we installed one as above and despite the same settings the iPad sleeps after about 30 minutes. At this latest install the iPad mini 4 is running iOS 12.
I did some research using my iPad mini 4, running iOS 12 at home (not in a wall mount), but plugged into the power. Again after about 30 minutes the iPad went to sleep.
Has anyone else come across this ? And is there a work around ?