Try it without the columns environment in your document, i.e.
\startchapter[title=\mytitle{Register}]
\placeregister[index]
\stopchapter
Hans van der Meer schrieb am 26.08.18 um 17:48:
Could the following setup I used be the culprit?
The real question is why do you get an index without two columns.
\starttext
\dorecurse{26}{\convertnumber{a}{#1}\expanded{\index{\convertnumber{a}{#1
\placeregister[index]%[n=3]
\stoptext
Hans van der Meer schrieb am 26.08.18 um 17:37:
How do I produce an index with more than one
How do I produce an index with more than one column?
This produces one column only:
\startchapter[title=\mytitle{Register}]
\startcolumns[n=2]
\placeregister[index]
\stopcolumns
Nor did \placeregister[index][n=2] or \placeindex[n=2], with or without the
