Something broke. I think there was no problem when I last visited a couple days ago. Today all posts have only a down arrow for the spillover actions, no icons. If I move the mouse above where the icons /should/ be, the pointer turns into a finger. So the actions are still available but just invisible.
(edit) when I use Firefox and enable displaying images, only then can I see icons. I normally use Ungoogled Chromium with images disabled (images dramatically increase my Internet costs). So I wonder if someone tried to get fancy and install images instead of icons from fonts.
You can try clearing you browser cache for this site, people have reported that this fixes it for a while.
I have today noticed for the first time this happening on my mobile browser, but sadly it lacks the nevessary debug tools to figure out what is going wrong.
I have a suspicion what might be the cause, but without a clear way to replicate and identify the issue, I can’t do a bug report for it.