I feel your pain. 
unfortunately, many people have gotten to this point over the years. It’s up to you whether you want to try to continue with SmartThings or move onto another system, but although they have continued to promise better reliability since the summer of 2015, they still have an MFOP (Maintenance free operating maintenance free operating period) of about two weeks.
http://thingsthataresmart.wiki/index.php?title=Bug:_First_Reports
That’s worth it to many people in order to get the flexibility and power of a SmartThings operating system, but not to everybody.
In my own case, because I have to pay someone else to do any maintenance, even just changing batteries (I am quadriparetic), I need an MFOP of at least six months and preferably 12. I don’t expect any system to be perfect, but I do need my home automation critical systems to hit this target. I get that pretty easily from a number of HA systems, including the hue bridge, Amazon echo, Logitech harmony, Lutron Caseta, apple’s HomeKit and even wink these days. But not ST. So I have moved all of my critical systems off of it for now.
I do continue to use ST for convenience notifications like a reminder that the guestroom window is open when rain is expected and the guest is away from the house. It just does that much better than anything else in its price range.
So different things work for different people. If you want to, you can start trying to diagnose some of the issues and work through one at a time, but While you can make some improvements, most of the issues are not local problems. They just have to do with the fragility of the platform design And the very high rate of change introduced.
But there’s definitely no point in raising your stress levels over it. Smartthings is what it is, and it is a fun and exciting system for many people. And if you want to build a Jetsons house, it definitely offers a huge amount of Power for relatively small investment in money. But, as you’ve noticed, it does require a significant investment in time, including time spent troubleshooting problems which mysteriously appear without warning.
There are lots of alternatives out there these days, just depending on your own needs, preferences, and budget, so it all comes down to what you need. Different things work for different people. 