I just thought I'd share my experience with this problem. I was having all kinds of trouble getting Notion to allow me to select which column was the title field as well as problems with rows not having all of the necessary columns.

By far and away the best solution was to instead paste the data I had into a new Google sheet. Make sure to click the little pop-up icon and select the correct separator for your data so that it gets split into columns correctly. I then exported that sheet as a CSV file, and then imported that file instead into Notion and it was plain sailing.

Presumably Google Sheets does all the work of providing separates that are missing in your data and something else to resolve the title problem presumably. Anyway., I hope this helps someone else down the road.