The issue has been closed
All popup windows inside of PRs (Reviewers, Assignees, Labels, etc...) get hidden behind the content in the main area. Have confirmed issue does not happen when Refined Github is disabled. This also only happens on Github Enterprise, does not happen on github.com

Also, in case it is relevant, we are running GitHub Enterprise Server 2.17.5

If it helps, also seeing this on GitHub Enterprise 2.15.3
, with refined-github 19.9.17
Tried disabling a number of individual features today in hopes of narrowing it down, but haven't had any luck.
Please let me know if there's anything I can do to help find the cause of or fix for this 🙂
posted by philmcardle over 5 years ago
I don't use Enterprise so it's hard to see what's wrong. Perhaps it's sticky-discussion-sidebar
but this issue can only be fixed if a GHE user sends a PR.
posted by fregante over 5 years ago
Oh, it is sticky-discussion-sidebar
🙂
posted by philmcardle over 5 years ago
posted by busches over 5 years ago 
I can have a look at this after work today :)
posted by Jarvvski over 5 years ago
Hi, maybe this helps! It looks like .discussion-sidebar
is missing position: relative
for z-index
to take effect. Once I add that, z-index is working:

https://<ghe url>/app/app/assets/stylesheets/components/discussion-timeline.scss
posted by kamranayub over 5 years ago
I've confirmed that @kamranayub solution does fix it. As a workaround, you can add this as Custom CSS in the add-on preferences:
.discussion-sidebar {
position: relative;
}
posted by jvtrigueros over 5 years ago
Can confirm that adding @jvtrigueros's CSS to the plugin custom CSS resolves the issue.
posted by mpaw over 5 years ago
posted by fregante over 5 years ago 
@fregante No, sticky-discussion-sidebar
does not work on GHE. Can confirm that disabling it also fixes the issue.
posted by mpaw over 5 years ago