I was not trying to sort "just" one column. I was trying to sort some rows, including all the columns labeled in the sheet.
Meanwhile I found the issue, and I wonder if you can tell me what happened: I had added a column before column A, gave it a name, but whenever I deleted or added rows, column A (Type) was unaffected. And sorting some or all of the document was impossible.
I deleted the new column and inserted a new column in between two of my original columns, and placed the new date in there. Everything works fine now.
Is it bc I had originally set up the spreadsheet as a table, so when I added a column outside its perimeter, that column wasn't recognized as part of the table?
Thanks!
(This is Lisakristel who first posted the issue. For some reason, Microsoft sent me to the registration page after I signed in, refusing to believe I am lisakristel, and set up a new screen name for me.)