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. 


}
  if ((OffscreenLane & lanes) !== NoLanes) {
    return_highestLanePriority = OffscreenLanePriority;
    return OffscreenLane;
  }
  if (__DEV__) {
    console.error('Should have found matching lanes. This is a bug in React.');
  }
  
  return_highestLanePriority = DefaultLanePriority;
  return lanes;
}
export function schedulerPriorityToLanePriority(
  schedulerPriorityLevel: ReactPriorityLevel,
): LanePriority {
  switch (schedulerPriorityLevel) {
    case ImmediateSchedulerPriority:
      return SyncLanePriority;
    case UserBlockingSchedulerPriority:
      return InputContinuousLanePriority;
    case NormalSchedulerPriority:
    case LowSchedulerPriority:
      
      return DefaultLanePriority;
    case IdleSchedulerPriority:
      return IdleLanePriority;
    default:
      return NoLanePriority;
  }
}