Just updated Discourse to version 2.6.0.beta4 (https://github.com/discourse/discourse/commits/500d22bf32a56a42da17c67eb4293368dc87d8ad) and an issue is now occurring where pages are getting cut off at the top.
For example, when I click into my profile
or at the top of a thread
Can you try loading your site in safe-mode with the 'Disable all site customizations" checkbox checked? If that fixes the issue, then the cause of the problem will be that an update in the core Discourse code is conflicting with your theme’s CSS. It should be possible to update your theme’s CSS to fix the problem.
This is due to a change we made to the header positioning. It looks like you have
position: absolute on
.d-header in your CSS, if you remove that line it should be fixed.