huuduy216 if the
rev-manifest.json file exists, Flarum will use the filename listed in that file.
rev-manifest.json files are deleted.
If there's a lot of traffic on the website, there might be a very small risk of race condition where two requests execute in parallel and delete each other files. For high traffic forums like those this extension might help https://discuss.flarum.org/d/23321-cache-assets
If all this happened but you didn't clear the cache or enabled extensions, it's probably another reason but I'm not sure what it could be.