The case seems to occur when the article has php code defined.
So you edit the article.
The PHP code is displayed as an ICON, so you click the Code View tab and the system hangs.
Looking at Firefox console you also get the error message below
You seem to be able to click on the Editor tab and then the Code tab again and it then works
Article without PHP seem okay
Chris
JCE 2.8.6 Pro, latest versions of Joomla and all extensions
ERROR MSG
TypeError: node.getAttribute is not a function 2 index.php:9:12920
nodeChanged https://www.stokeandnewcastleramblers.org.uk/administrator/index.php?option=com_jce&task=editor.pack&context=22&50a4186199b82264d629824f6479a721=1&ff85c523d851eb6bb21256cb6220ef5d:9
nodeChanged https://www.stokeandnewcastleramblers.org.uk/administrator/index.php?option=com_jce&task=editor.pack&context=22&50a4186199b82264d629824f6479a721=1&ff85c523d851eb6bb21256cb6220ef5d:9
bindNativeEvents https://www.stokeandnewcastleramblers.org.uk/administrator/index.php?option=com_jce&task=editor.pack&context=22&50a4186199b82264d629824f6479a721=1&ff85c523d851eb6bb21256cb6220ef5d:9
dispatch https://www.stokeandnewcastleramblers.org.uk/administrator/index.php?option=com_jce&task=editor.pack&context=22&50a4186199b82264d629824f6479a721=1&ff85c523d851eb6bb21256cb6220ef5d:1
eventHandler https://www.stokeandnewcastleramblers.org.uk/administrator/index.php?option=com_jce&task=editor.pack&context=22&50a4186199b82264d629824f6479a721=1&ff85c523d851eb6bb21256cb6220ef5d:9
executeHandlers https://www.stokeandnewcastleramblers.org.uk/administrator/index.php?option=com_jce&task=editor.pack&context=22&50a4186199b82264d629824f6479a721=1&ff85c523d851eb6bb21256cb6220ef5d:3
defaultNativeHandler https://www.stokeandnewcastleramblers.org.uk/administrator/index.php?option=com_jce&task=editor.pack&context=22&50a4186199b82264d629824f6479a721=1&ff85c523d851eb6bb21256cb6220ef5d:3
.