To reproduce:

1. Create to a quiz
2. Add at least 2 questions to the quiz (can be new questions, or from question bank)
3. Make sure editing mode is enabled
4. Hit F12 to view dev tools and open the console
5. Try to drag one of the questions to another page in the quiz
   Expected: You're able to
   Actual: You see console errors

   Uncaught TypeError: this._dimCache is null

   _checkWinScroll http://localhost/testmaster/theme/yui_combo.php?3.18.1/dd-ddm/dd-ddm.js&3.18.1/dd-ddm-drop/dd-ddm-drop.js&3.18.1/dd-proxy/dd-proxy.js&3.18.1/dd-constrain/dd-constrain.js&3.18.1/dd-drop/dd-drop.js&3.18.1/dd-scroll/dd-scroll.js&3.18.1/dd-drop-plugin/dd-drop-plugin.js&3.18.1/dd-delegate/dd-delegate.js&m/-1/core/notification/notification-alert-debug.js&m/-1/core/notification/notification-confirm-debug.js&m/-1/core/notification/notification-exception-debug.js&m/-1/core/notification/notification-debug.js&m/-1/core/dragdrop/dragdrop-debug.js&m/-1/core/blocks/blocks-debug.js:2076

   align http://localhost/testmaster/theme/yui_combo.php?3.18.1/dd-ddm/dd-ddm.js&3.18.1/dd-ddm-drop/dd-ddm-drop.js&3.18.1/dd-proxy/dd-proxy.js&3.18.1/dd-constrain/dd-constrain.js&3.18.1/dd-drop/dd-drop.js&3.18.1/dd-scroll/dd-scroll.js&3.18.1/dd-drop-plugin/dd-drop-plugin.js&3.18.1/dd-delegate/dd-delegate.js&m/-1/core/notification/notification-alert-debug.js&m/-1/core/notification/notification-confirm-debug.js&m/-1/core/notification/notification-exception-debug.js&m/-1/core/notification/notification-debug.js&m/-1/core/dragdrop/dragdrop-debug.js&m/-1/core/blocks/blocks-debug.js:2178

   bind http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:12425

   _notify http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:13760

   notify http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:13789

   _notify http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:13452

   _procSubs http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:13578

   fireComplex http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:27628

   _fire http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:13525

   fire http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:14658

   _align http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:40587

   _alignNode http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:40605

   _move http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:40702

   _move http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:39341

   bind http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:12425

   throttle http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:39078

   _notify http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:13760

   notify http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:13789

   _notify http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:13452

   _procSubs http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:13578

   fireSimple http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:13545

   _fire http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:13527

   fire http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:13496

   fn http://localhost/testmaster/theme/yui_combo.php?rollup/3.18.1/yui-moodlesimple.js:20472

If you try to drag the same question again, it works without errors, however. I also saw a difference in behaviour when trying this without editing mode enabled - so that may be worth investigating too. I noticed this in quiz, so have tagged it as quiz and javascript. This may turn out to be purely a drag and drop js-related issue though. I can't say for sure yet.

The same error can be also reproduced with the Feedback module. More information can be found in MDL-80417 (which has been closed as duplicated because of this issue).