I may be wrong here, as I have never worked on communities, but how was
.myAccount{ display:none; }
working before. When i inspect element in my community page, i see each menuitem
written as home uiMenuItem
, profile uiMenuItem
. Though I cannot see My Account
as I dont have certain permissions.

But I went ahead and from advanced setting of community builder edited the Head Markup
to put this css.
<style>
.profile.uiMenuItem{
display: none;
}
</style>
And it hides the My Profile
section from the menu, May be if you can change the profile to whatever class name account has, that might work.