If I set the with of the submenu of the vertical menu in:
Mega menu -- Menu item settings -- Mega setting -- Wrapper width. The box gets wider but the text of the submenus stays the same! and does not get wider.
I am sorry for not getting your points. It would be awesome if you can possibly include URL of your site and a screenshot with detailed explanation. I am happy to help you out.
Also You can refer the guide: https://www.ubertheme.com/docs/ub-mega-menu/
I received your additional clarification via email. I tried to log in your site, yet it seems you’re logging in as well (http://prntscr.com/g8mglu)
Kindly hold on all activities at your end, so that I could check the issue you mentioned. Magento 2 enhances security layer, which allows 1 account to access your backend only.
Please open the file app\design\frontend\Ubertheme\megamall\Ubertheme_UbMegaMenu\web\css\source\module\_vertical.less, navigate to the line 155 and remove the line: width: 33.33% !important;
Once done, please re-compile LESS to CSS.
Make sure you remove the var/* and pub/statics/* and clean the cache.
Please let me know how it goes then.