I'm not sure how the situation looks now, but I remember Hermes had problems with this construct, hooks weren't firing properly and I had lots of trouble debugging this. The solution was to use curly braces instead of a void-returning expression.

Could you check if this works correctly now? By e.g.

const foo = () => { console.log('unmount'); };

// in hook
return () => foo();

Or simply apply the suggestion without investigation, to save time

Is there a reason we can't just return subscription.remove? Is this not bound for it?

Is there a reason we can't just return subscription.remove? Is this not bound for it?

Yes, Flow is complaining

Cannot get subscription.remove because property remove [1] cannot be unbound from the context [2] where it was defined. [method-unbinding]

@bartek I'm applying your suggestion. Wondering what were the issues you've faced.