Hi @ravanh,
I tested with Chrome (62.0.3202.94 (Official Build) (64-bit)) and Firefox (57.0) with the same issue. Inspecting it appears all the break elements have a display none forced on them;
.options-media-php br {
display: none;
}
Looking into the Code it appears that’s from wp-admin/css/common.css;
.options-media-php br {
display: none;
}
@media screen and (max-width: 375px) {
.options-media-php input[type="number"][name*="_size_"] {
margin: 5px 0;
}
.options-media-php label[for*="_size_h"]:before {
content: '';
display: block;
}
.options-media-php br {
display: block;
}
}
Reference: https://github.com/WordPress/WordPress/blob/f4e974057ea98ad98b1d8f7173f35bda2e5ef1c3/wp-admin/css/common.css#L3934
This seems to have been introduced in 4.9 as it’s not present in 4.8.3
I can’t find the trac or exact commit but that seems to be the issue. So they (WP) made a decision to use br as mobile-only break. So maybe a best solution for them would have been to setup a class like .mobile-break and be specific with it, maybe worth a Trac ticket.
Let me know if you need anything else,
Cheers