This is indeed weird. I cannot imagine that this has been broken for long, much less that it was always broken. I found the issue is that at the initial setup of the control stage, the Remote Interfaces are still the base ones provided by Factorio. Since I was storing that in a boolean for checking the rest of the time (since I don't think would change during runtime, after initialization), it - and all used Remote Interfaces - was always false, so we never attempted make the actual calls.
The fix is simple, and I'm not sure it's a big enough performance impact to justify going back to caching the value (and potentially having inconsistency issues). However, I would be that these behaviors changed in recent Factorio updates, but I don't know if it's a bug or expected.
