Most likely the problem is related to browser caching. You said the the site worked fine for a while, then after a period of time it started no to. What likely it happened is that the web browsers cached the good .js and .css files for a period of time (depending on the browser settings), and even if the latests .js/.css files are broken those browsers didn’t picked up these files until recently.
This is why you didn’t notice the problem before, and this is why the same browser and the same site no longer work, even if before they worked and no changes were made since then.
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solved Website formatting going haywire automatically