Into no needed, I will prove by my work.
Give me the website link, I will be shorted out within 30 mins
I think when you customize the theme, you put extra height and width, it's going to the submenu that's why when you go for submenu than submenu disappears.
I don't need any access, honestly, I have great knowledge in Magento 1 and 2, i can upload by myself.
But it's better to take over this part.
Thanks, Best regards
Mehebub Jahedi