This PR, or something similar, is a partial fix.
https://github.com/discourse/discourse/pull/3795
I am fairly certain that for forums that are not using a custom header it is safe to set
.d-header{position: fixed;} as both a desktop and a mobile customization. That will keep the header fixed to the top of the screen on ios devices.
For forums that do have a custom header, one possible workaround, combined with this PR, is to set the forum’s body background color to match the custom header’s background for small screens.
