I've looked better into megamenu configuration in database and fixed the menu by removing unnecessary rows on top of submenus :)
I know that it's easy to edit megamenu in backend, but with 1.2.1 I'm getting error with paths to t3-assets etc. - well, this is fixed in 1.4.3 of course, but when I upgrade to 1.4.3, my menu is flickering (I don't want any slide/fade effects, just stay open while moving between menu items).
I had something like this:
{\"item-103\":{\"sub\":{\"rows\":[[{\"item\":342,\"width\":12}],[{\"position\":108,\"width\":4},{\"position\":107,\"width\":4},{\"position\":109,\"width\":4}]]}
and just removed unnecessary row to make it like this:
{\"item-103\":{\"sub\":{\"rows\":[[{\"position\":108,\"width\":4},{\"position\":107,\"width\":4},{\"position\":109,\"width\":4}]]}
but anyways, thanks for support