I am currently customising the Dawn theme and I am facing layout problems. I did changed some lines of codes but I only modified CSS and didn't touch to the liquid tags. When I search for products and a lot of results show up, there is no problem product cards appear as expected but when only 1 or 2 product appear, for a reason or another the product card appear very small and I don't know what's causing this.
In the future when reference page bugs in screenshots be courteous of others time and provide direct urls and don't make others hunt and peck through screenshots to figure out reproduction terms in search.
If not a pre-existing bug you may just be missing something like a width:100%; somewhere or relevant class name on the search results container.
Otherwise you should do a file compare of current CSS file and any backups to try and localize the cause.