I can’t say whether there’s an easy fix, as others have suggested, when troubleshooting issues on an individual account you just have to pick a device to start with and work your way through.
One hopeful note: smartthings is right in the middle of a huge transition from a largely cloud-based system to one which will operate much more locally, both with edge Drivers and potentially eventually with matter support.
They could still screw up the app, of course. (For example, they didn’t have to make the current app reliant on the cloud, but they did.) So there’s no way to know for sure that things will get better on that front. But I think it’s reasonable to hope that they might with all the changes that are coming.
All of which is to say: I certainly understand somebody deciding to jump ship right now if the frustration level is just too high. But I can also understand somebody feeling mildly optimistic that things will be better by the end of this year. I know that’s a long ways away for something that you use every day, but if you have a big investment in money and time in your existing setup, some people will think it’s worth waiting to find out.
I am at the point where the app is now completely unusable for me because it’s not voice navigable. The last time it was truly useful was I think in early 2018. Since then, I’ve been reporting the issues with every new release, and I’ve received multiple assurances from multiple staff members that it would get better, at least meeting the W3C minimum accessibility requirements, but it still doesn’t. 
I know that only affects a very small percentage of people, but it’s a small group of people who have a very significant use for home automation, and other competing platforms have found it a reasonable target market. But so it goes.
Anyway, only you can decide what will be best for you. There are a lot of choices right now, and a lot of changes coming for everybody industrywide with the potential release of Matter. Personally, I wouldn’t be investing a lot in anything new right now until we see whether Matter can deliver this summer, but again, that’s a personal choice.
Good luck, which ever way you go. I hope you find a system that works well for you.