As many said yesterday, SmartThings does well in some areas while it fails in others. Unfortunately, you just stepped on the bomb. Using schedules is not SmartThings’ forte. If reliability factor is important to you, then I suggest paying close attention to your return window. But if the cool factor is important to you (with questionable reliability) then just find a way to limit hard schedules for your automations. There are many other options that have proved to be more reliable in the SmartThings world (lux level, IFTTT integration, offsetting sunset/sunrise times, etc).
BTW, if you are looking to dim lights based on modes/lux, you might find @Mike_Maxwell’s app very useful. Been using it it for months with great results…