There's nothing wrong. The watch measures stress whenever it can, but high activity often makes it impossible. But if the stress can be measured, it doesn't matter whether MoveIQ detects something or not. Is there a reason you think it could be a bug?
Well, doesn't that affect stress score for the entire day then? But maybe that is not used for training readiness calculations etc, only nightly HRV that matters there?
I think that all registered physiological stress affects training readiness, and it should. And the HRV status is different from stress, they are shown as separate factors for training readiness.