Definitely seeing this on enwp and eswp on monobook, but not vector. (And I ain't logged in, this is just with useskin.)

Cannot replicate locally on monobook master, though, so either it's already been fixed or the problem is being caused by something else entirely...

Okay, checking out the same commit, I seriously cannot replicate this. The styles are there, locally. They're just plain not there on wikimedia?

Scratch that I can't get this version of core to work at all because... vendor doesn't appear to be up to date? I dunno, none of this makes any sense to me, I'm at the end of my rope.

(Don't worry, though, someone with half a brain should look at this at some point and they should be able to figure it out. >.>)

...okay, because this was nagging at me and weird and I realised what I did wrong the first time, I went and corrently checkout out the deployed core/extensions/whatever pile currently live on wikimedia (rMW340b2be45285), and... nope, still can't replicate locally.

Definitely seeing it on wikimedia, though! This is so weird!

I can reproduce just fine with core 4365aa0 and monobook 27e5bd2.

Can't see anything related to external link icons:

Reverting MonoBook 747c8e6 causes the stylesheet to appear, but the icon still isn't there, probably due to 63c4125

Change 649424 had a related patch set uploaded (by Jdlrobson; owner: Jdlrobson):
[mediawiki/skins/MonoBook@master] Restore external links to responsive monobook

https://gerrit.wikimedia.org/r/649424

Please disable "Enable responsive MonoBook design" to workaround this bug.

Change 649424 merged by jenkins-bot:
[mediawiki/skins/MonoBook@master] Restore external links to responsive monobook

https://gerrit.wikimedia.org/r/649424