Unfortunately, your page design is too crowded, as the warning shows:
Overfull \vbox (12.0pt too high) has occurred while \output is active [2]
Class memoir Warning: The material used in the headers is too large
(24.0pt) for the given head height (12.0pt), it is recommended to
either increase the head height or redesign the header
(in both cases you will find help in the memoir manual). on input line 14.
While, technically, your use of \settypeblocksize and \setulmargins is impeccable, the end result (I did this on A4 stock and page size) is that there isn't enough space in the header to accomodate your long title.
There are a number of different ways to fix this, most of which will change the proportions of the typeblock, which, I recognise, you may not want to do.
However, since a long title in the page header probably isn't essential, you might want to try using a short title for the header and TOC:
\chapter[Shorter Title]{{Lalala lalala lalala lalala
lalala lalala lalala lalala lalala lalala lalala lalala lalala lalala}}
If you need the long title in the TOC, then something like this will work, but is rather brittle:
\chapter{Lalala lalala lalala lalala lalala lalala
lalala lalala lalala lalala lalala lalala lalala lalala}
\markboth{Short chapter title}{}