When editing a secret in the popover, the linking dialog opens and you can insert a link by pressing enter, but the list of suggested articles is about 3 pixels high, so you can't actually see what you're doing.
Also tried in Chromium, and it happens there too. It does not seem to be browser-related.
Which editor does this seem to be happening in?
Inside the Edit Secret popover, are you seeing Advanced (Euclid) or Visual editor? (If you see a column that has line numbers, that is Advanced - otherwise it should be Visual instead).
Edit: It looks like this issue is present only within the Visual editor. I will investigate the cause.
I see there is a small bug with positioning of the suggestions modal box. I am working on a hotfix for that, but the list is no longer collapsed!