Thanks for writing in! Are you using CloudFlare or may have installed a caching plugin like WordFence, W3 Total Cache or WP Super Cache? Please keep in mind that after doing every updates, always remember to clear all caches when updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
I found out it’s interfering with superfly menu (the buttons need more margin right and left in order to work). Maybe good to know since superfly will be a part of X..