Happening since today ~17:00 UTC. See for instance https://tools.wmflabs.org/guc/?user=126.96.36.199 and compare with https://it.wikipedia.org/wiki/Speciale:Contributi/188.8.131.52. Wikidata (at least) is working per e.g. https://tools.wmflabs.org/guc/?isPrefixPattern=1&src=rc&user=5.90.
I wonder if this has to do with the recent switch to read new/write new for the actor table (T188327) and T224440
Addendum: Apparently, it stopped working for wikidata, too.