The root cause of the default opening issue is that the current page URL is matching the opened menu item link. The accordion menu will open the item if its link is matching the page URL.
The amenu.close() has animation and there is no workaround to turn it off.
If the page URL does not exactly match the opened menu item, but similar, the amenu will take it as the best fit and open it. You can add an menu item that match better to the current page URL, and set the menu item invisible(<li style="display:none;">...</li>. Then you won't see the open and close.