From enwiki feedback:
I was huggling in eswiki when suddenly and edit from simplewiki appeared and i tried to revert it, giving https://simple.wikipedia.org/w/index.php?title=Microvillus&diff=prev&oldid=5621093 this result. Any ideas? -- User:Jcaraballo 18:09, 4 March 2017 (UTC)
Seems like there was a serious problem with data consistency, needs further investigation, hardware / OS related issue seems extremely unlikely, probably a bug in code.
Same problem tonight with French+English projects. Nothing particular to note, using last version from git, I was in a run test to verify small edited interface code which is nothing special.
https://fr.wikipedia.org/w/index.php?title=Sp%C3%A9cial:Contributions/Framawiki&dir=prev&offset=20170715210252&limit=13&target=Framawiki
Since as a patroller I can't see that I replace French page content with English one, I raise the priority.
I successfully managed to reproduce this issue, it requires software rollback to be enabled.