It’s definitely not just you, but different people have different experiences. 
SmartThings allows you to use many different devices from many different brands, but that’s always meant more rough edges than platforms that restrict your device choices more.
And the ST design philosophy has always meant a lot of undocumented changes which can be confusing even if they’re working as the company intended. 
It’s also possible there’s some specific local issue with an individual device, either a weak mesh or local interference.
If you like, we can take one problematic device at a time and see if there’s any fine tuning that can be done to improve its reliability. But we’ll need to know the exact brand and model. And that kind of troubleshooting can be tedious, with no guaranteed improvement. So it’s up to you.
If you do want to start troubleshooting individual devices, start by reading post 11 in the following thread. (I’ll link directly to it.) then go up to the top of that thread and read the whole thing. After that, come back here and give us a specific brand/model that’s acting flaky and we’ll start with that. A screenshot of the routine, if any, would also help.