When the bot submits its move too quickly after getting the previous move, the UI seems to get confused; the server stores everything ok but the first action is not displayed.
Specifically, when the AI plans a place+slide combination, and submits the place, awaits response, then submits the slide immediately, the UI doesn't display the placement; but a page reload shows the correct board. When a 0.5s delay is added before submitting the slide, the UI displays everything just fine.