After updating react-dom to version 17 the build now includes Array.fill() which isn't supported by ie11 without polyfilling. Coming from this line. Tested with just the default cra production build to make sure it wasn't a problem with my webpack config and the same issue.

https://github.com/facebook/react/blob/96ac799eace5d989de3b4f80e6414e94a08ff77a/packages/react-reconciler/src/ReactFiberLane.js#L671

Tested using CRA on version 16.9.8 of react and react-dom which works with the production build for ie11. 


export function lanePriorityToSchedulerPriority(
  lanePriority: LanePriority,
): ReactPriorityLevel {
  switch (lanePriority) {
    case SyncLanePriority:
    case SyncBatchedLanePriority:
      return ImmediateSchedulerPriority;
    case InputDiscreteHydrationLanePriority:
    case InputDiscreteLanePriority:
    case InputContinuousHydrationLanePriority:
    case InputContinuousLanePriority:
      return UserBlockingSchedulerPriority;
    case DefaultHydrationLanePriority:
    case DefaultLanePriority:
    case TransitionHydrationPriority:
    case TransitionPriority:
    case SelectiveHydrationLanePriority:
    case RetryLanePriority:
      return NormalSchedulerPriority;
    case IdleHydrationLanePriority:
    case IdleLanePriority:
    case OffscreenLanePriority:
      return IdleSchedulerPriority;
    case NoLanePriority:
      return NoSchedulerPriority;
    default:
      invariant(
        false,
        'Invalid update priority: %s. This is a bug in React.',
        lanePriority,