Adding another menu in 5.0-rc1 not work correct.
Menu is created, but you could not add pages in it.
Just message appears "oops(Current menu not set)" when switch to it.
ps. I'm soon going to publish plugin update, that uses additional menus to group pages, so it would be good to not change additional menus naming and saving)
and where is better to report issue here or on github?
edit: Also "addon text" command do not work it used in simple blog for example
may be should different used it