The issues you have with the TODO Macro are most probably caused by the fact that the macro produces invalid HTML which is not expected by the WYSIWYG editor. This is Loading... . Note that the TODO Macro is a contributed extension that is not supported / recommended by the XWiki Development Team. Ping @ludovic but he probably doesn’t have the time to fix the macro.
Regarding playground.xwiki.org , the error is due to an unfinished upgrade of the CKEditor. We’ll fix this ASAP. Ping @vmassol . Thanks for reporting.