I've been experiencing this too. Most commonly when I'm converting an unstructured reference to a template and have left some non-template text in the reference content.

@DragonflySixtyseven mentioned in #wikipedia-en on freenode an off-wiki complaint that https://en.wikipedia.org/wiki/Jeddah_Tower had a popup with vandalism in it. That popup showed an old revision of Skyscraper design and construction from 3 days ago that was quickly reverted. I confirmed using the REST API that the old revision was still being used as the summary. I then purged the page (using the UTC purge clock) and re-sent the API request. The API returned the newest revision, which is also what was shown by Popups.

It only occurred while logged-out. As I said in the original description, the issue disappeared for me before I could properly investigate.

@Aklapper They report that other dark DE themes (Adawaita-Dark and Equilux) still have the issue. Light and default themes do not.

OS - (uname output) Linux 4.19.67_p2-debian-sources-lts x86_64
DE - XFCE 4.12
Theme - Vertex-Dark (https://github.com/horst3180/vertex-theme)

(@Aklapper I used the task template linked on https://meta.wikimedia.org/wiki/Wm-bot#Support, which auto-assigns.)

I will say that OTRS session timeouts are much less annoying than ACC session timeouts because OTRS will return you to where you left off (assuming that you weren't writing something, of course).

This might be something worth looking at after 2fa becomes unbroken and available. (T122220)

They returned today saying that the issue went away at about 15:40 UTC, but was still occurring around 12:00 UTC.

Oops. Sorry.

Reported again via OTRS Ticket#2019021810005137. After mentioning the problem in #wikimedia-tech on IRC, most were able to reproduce the issue while another was not (see logs).

Looks like this was fixed upstream 5 months ago? https://gitlab.gnome.org/GNOME/librsvg/issues/74 and https://bugzilla.gnome.org/show_bug.cgi?id=786372#c7 got closed as fixed.