Hi all,
I am experiencing the same issues, and have actually opened a separate topic with a more detailed description. (see here, also UK based)
One important hint / quick fix: It seems that all the issues only occur for SmartApps on the SmartThings platform. I have recreated some of the (mode dependent) functionalities in SmartRules (which also runs the routines in the SmartThings cloud), and all of them have performed reliably (so far… 
)
Let’s keep fingers crossed and see what the firmware update will do… 