Exception in your example app: The provided ScrollController is currently attached to more than one ScrollPosition.

[JanZeman]

Repro steps:

1. Run your sample app via flutter run -d windows
2. Scroll down to let's say line 500 on the first yellow tab
3. Scroll up and QUICKLY switch to the second red tab
4. Keep trying there and back - usually I get it reproduce within 30 seconds.

`══╡ EXCEPTION CAUGHT BY ANIMATION LIBRARY ╞═════════════════════════════════════════════════════════
The following assertion was thrown while notifying status listeners for AnimationController:
The provided ScrollController is currently attached to more than one ScrollPosition.
The Scrollbar requires a single ScrollPosition in order to be painted.
When the scrollbar is interactive, the associated ScrollController must only have one ScrollPosition
attached.The provided ScrollController must be unique to one ScrollView widget.

When the exception was thrown, this was the stack:
0 RawScrollbarState._debugCheckHasValidScrollPosition. (package:flutter/src/widgets/scrollbar.dart:1492:9)
1 RawScrollbarState._debugCheckHasValidScrollPosition (package:flutter/src/widgets/scrollbar.dart:1517:6)
2 RawScrollbarState._validateInteractions (package:flutter/src/widgets/scrollbar.dart:1428:14)
3 AnimationLocalStatusListenersMixin.notifyStatusListeners (package:flutter/src/animation/listener_helpers.dart:240:19)
4 AnimationController._checkStatusChanged (package:flutter/src/animation/animation_controller.dart:815:7)
5 AnimationController._startSimulation (package:flutter/src/animation/animation_controller.dart:749:5)
6 AnimationController._animateToInternal (package:flutter/src/animation/animation_controller.dart:612:12)
7 AnimationController.reverse (package:flutter/src/animation/animation_controller.dart:495:12)
8 RawScrollbarState._maybeStartFadeoutTimer. (package:flutter/src/widgets/scrollbar.dart:1625:37)
12 _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:184:12)
(elided 3 frames from class _Timer and dart:async-patch)

The AnimationController notifying status listeners was:
AnimationController#f54e4(◀ 1.000)
════════════════════════════════════════════════════════════════════════════════════════════════════`