I have a Honeywell TH6110D1005 thermostat. I do not use the program mode, I keep my temp set to 71° at all times when it is on the Cool setting.
Sometimes, it resets itself to 65° for no reason whatsoever. I have replaced the batteries with new red Duracells but it happened again.
It is intermittent and it can go weeks without doing this.
I can't figure out why it is happening.