Itās very frustrating, but it has unfortunately happened to most of us. 
There have been many threads in the forums over the last year or so discussing issues with the reliability of SmartThingsā schedulers. After several attempts at fixing different parts of it, the company has now announced that they intend to replace the scheduler entirely. The CEO just said today that the new scheduler will go into beta testing in a few weeks. No timeline for when it might be delivered to everyone yet. We can all hope it will improve the reliability of the system.
29 days of SmartThings! Evaluated! - #32 by alex .
The good news is that the engine behind scheduled and triggered SmartApps (which includes Routines as well which are just another type of SmartApp from the perspective of the platform) will be totally replaced over the coming weeks. Our support team will have the ability to turn it on in beta for specific accounts, so those on this thread who are interested could help us to get it fully tested more quickly.
If you are interested in reading other discussion threads on the topic, just browse the general discussion sub category, or search for āreliability.ā As I said, there have been many discussions.