I don't use 2016 (yet), but I can offer one or two general suggestions.
Anytime you experience a problem of this kind, think like a detective. Rather than proceeding to do all the work all over again, test the function to determine the cause of the problem before committing more effort that may be lost.
The first thing to do is to display hidden characters, to show you what may be at work "behind the scenes." Click on the backwards P on the Home tab; clicking it again toggles it off. What we're looking for is the needed section breaks required for multi-column work, unless the entire document is, for example, 2-column. In order to separate a one-page from a multi-column page, a page break will not work; you need a Next Page Section Break. Breaks of various types are listed on the Page Layout tab; use the down arrow beside breaks.
Note that a section (one page or more) of multi-column between two single-column or multi-column of a higher or lower number (e.g., going from 2-col to 3-col) requires a break both before and after, because columns are a section property, not a paragraph one.
A Continuous section break allows, for instance, setting two columns in the middle of a single-column page, but this can get tricky. In any case, I still advise displaying hidden characters to allow seeing if the breaks are there (a dotted line with "Section Break" and its type centered in it. If you save the document and then open it again and the section breaks have disappeared, that is another issue, probable corruption.
Also note, that another way to create multiple columns, without section breaks, is by using borderless tables. You can view the non-printing borders as dotted lines by selecting View Gridlines at the bottom of the drop down list by Table borders on the Home tab.