Ipad not Auto Lock/Sleeping after 16.6 update in Guided Access Mode

It seems like this issue has happened before where an iOS update happens and now, my twin sons use their iPad 9th gen devices for AAC voices and they won't go to sleep automatically no matter how we have them set. We have to put them into guided access mode to prevent two 4 year olds from locking the tablets out. But if they are in guided access mode they won't sleep and therefore the batteries drain quickly and they lose their voice before the end of the school day. Apple please address why we can't have the sleep function working while in guided access mode? It worked prior to this update recently and now it doesn't.