On iconic logo designers, a great website by the designer David Airey with a collection of logo designers, I found the following multicolumn list:

In books the multicolumn format for lists was generally used to save space. A single-column lists takes up a lot of vertical space and only little horizontal space. A long list could be split in the middle to be shown in two columns, or split at multiple points for more than two columns.
In this example there are 32 items: 4 columns, each containing 8 items. These items are ordered alphabetically (based on the designer’s last name). The table was filled row by row.
Reading order
However, in general a column-first reading order feels more natural. In this list, the items in each column are centered horizontally, which points more attention to the vertical direction than to the horizontal rows.
The same list, filled column-first:

The alphabetic ordering is discovered faster, and it’s easier to find a particular item.
General guideline
When placing items in multi-columns lists or tables, follow the natural reading direction unless there is a good reason to do otherwise. This one is pretty obvious. That in html it is easier to fill a table row by row does not count as a good reason.
Hi Marielle,
Many thanks for this post.
You pick up on a point that was bugging me. Thing is, because the list is being amended on a daily basis, I was waiting until a more final point before using the order you mention.
Do you know a straightforward way to get around this?
All the best.
I like your work here and wanted to know if you have any data and/or citations which support the information…?