saguaros Thanks again for your help Saguaros!
It's important to note that Brickwork's current demo-template behaves perfectly. Even when checking with Chrome's Developer Tools, the demo's related image resizes automatically no matter when or how the width changes, without needing to refresh the page.
As for the cause/history of this problem, I originally installed an older version of the quickstart-template, and though the image was resizing correctly when refreshed, the break when resizing did already happen back then. When I noticed the demo-template didn't have this problem, I decided to update the template assuming the resizing issue was ultimately fixed via the template. Alas, it worsened the problem as now the image/layout was broken permanentanly (even after refreshing). I explored updating the module itself, but didn't succeed. I even considered reinstalling the quickstart-template; but having never done that before, I didn't know if that might impact/destroy the existing website. I ultimately spent countless hours exploring css solutions, but couldn't figure it out. Thus the need to ask for expert advice.