Make sure the sort order is set to filename rather than Added order. I don't want everyone's Lightroom behaves the same, but Lightroom seems to like to switch to Added order whenever I import. I always have to remember to change it back to filename because that is what I prefer.
Thank you for your message. It started me thinking about what to do. I found that when I make sure to check "add to catalog" the images show up side by side.