Hey!
This is to be expected with the current Kotlin Coroutines memory model.
The moment an object (in this case your mutable list) is passed between different coroutines, it is frozen and cannot be mutated. Attempts to do so will cause exceptions such as the one you’re experiencing.
The way around this particular problem, using Orbit, is to make that list part of the state. Reductions are not subject to mutability exceptions.