Bad news: PM notifications was completely broken
Good news: fix message notification not being shown · streetcomplete/StreetComplete@1a97dfc · GitHub fixes it
Bad news: it needs to be released, fixing code in repo is not magically updating all deployed apps
Thanks for testing to @SomeoneElse
(debugging this and block messages took multiple hours, even if this change is tiny. I fixed a related bug concerning HTTP codes while doing this. Block message not being shown loook more and more like osm.org bug and responsibility, expecting every editor app to include complex hacky workarounds seems like a poor idea.)