"React has detected a change in the order of Hooks" but Hooks seem to be invoked in order

I am trying to use Context and Reducers via React's hooks, and running into problems with the order of the hooks not being constant. My understanding was that as long as the order of the useHook(…) remained the same, it was fine to invoke the returned state/update function/reducer in any sort of control flow. Otherwise, I'm invoking the hooks at the very beginning of the FunctionComponents.

Is it that I'm generating Days in a loop? Or missing something else?

Warning: React has detected a change in the order of Hooks
called by Container. This will lead to bugs and errors if not fixed. For
more information, read the Rules of Hooks:
https://reactjs.org/docs/hooks-rules.html

   Previous render            Next render
   ------------------------------------------------------
1. useContext                 useContext
2. undefined                  useRef
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The full version of Container is below. An excerpt from Day is below, and has a ref from react-dnd's useDrop.

export const Container: FunctionComponent<Props> = () => {
  let events = useContext(State.StateContext)
  //let events: Array<Event.Event> = [] <- with this, no warning

  const getDaysEvents = (day: Event.Time, events: Array<Event.Event>) => {
    return events.map(e => {
      const isTodays = e.startTime.hasSame(day, "day")
      return isTodays && Event.Event({ dayHeight, event: e })
    })
  }

  let days = []
  for (let i = 0; i < 7; i++) {
    const day = DateTime.today().plus({ days: i })
    days.push(
      <Day key={day.toISO()} height={dayHeight} date={day}>
        {getDaysEvents(day, events)}
      </Day>
    )
  }
  return <div className="Container">{days}</div>
}

An excerpt from Day (Event similarly uses a useDrag hook, also called at the top level just like here).

const Day: FunctionComponent<DayProps> = ({ date, height, children }) => {
  const dispatch = useContext(State.DispatchContext)
  const [{ isOver, offset }, dropRef] = useDrop({
    // …uses the dispatch function within…
    // …
  })
  // …
}

from "React has detected a change in the order of Hooks" but Hooks seem to be invoked in order