Hello,
I don’t know why the mega menu disappeared but I’m 100% sure that there were not any issues with it after the update and my first message to check the site, I checked that a few times and even told you to change the links because custom links were wrong. You can use the previous way also, but the Static block allows to align items nicely than the default way. Anyway, if you prefer the default way you can use it.
Regards