Make sure to clear all layers of site cache, as well as the CDN cache. If something else might be conflicting, you can also try this custom CSS:
.asp_m {
min-width: 500px;
}
@media only screen and (max-width: 768px) {
.asp_m {
min-width: 100%;
}
}
If nothing works, then can you please share a URL where I can check this issue. Back-end details would be also nice, so I could check if everything is working correctly.