What errors do you get?
Check the Global settings > Features tab, you can set category order option there

The global settings are already on manual ordering of categories. This does not however, translate to manual ordering in the widget. (I note in the file it has main cat ID, as orderby)

I can't recall what the error is, I'll have to test it again and post the result later. I believe all I did was change the file so that it said 'priority' after the orderby. It's likely I simply broke it because I couldn't remember what to type to change the order.

You probably selected "random", I remember there was a bug some time ago.

I'll see if this is already fixed in v4 and let you know.

Yes, blog settings are to show the posts randomly. The widget settings are:
block title, none
link to blog, no
item type, default
follow main list, no
blog id, [blog id]
group by, category/chapter
order by, title (changing to explicit order changed order of items, NOT order of categories)
direction, asc
max items, 20
link titles, auto
the rest are blank.