I have a triple (soon to be quad) on my cargo bike. But, haven't built the custom derailleur mount yet, so I've just been shifting manually. However, every once in a while I look down and it seems to have jumped from the big ring to the middle ring on its own.

Apparently the taller tooth profile for SS sprockets helps.
You can build a chainguard sandwich which will help.
If you use a SS rear, or IGH rear, then set the chainline straight and set the chain tension so the chain doesn't drop.