While trying to upload changeset 33193763, I met this message:
Error message(untranslated): Placeholder node not found for reference
-13644 in way 48378769
As it's difficult to debug this from within JOSM, I saved the *.osm file
and looked for that -13644.
I found it twice in updates to two landuse=forest ways.
I swear I did not update landuses, but I can't tell if one was attached
to something like a way I touched up as it is their pesting habit.
Anyway, it's not a reason for a dangling ref.
I edited out those 2 ways updates, I attached them to this ticket, I
reloaded the purged *.osm file and then the chngeset uploaded correctly.
Hoping this can help.
André.