Why has my daily update stopped working?

I have a daily cron job that updates the Great Britain extract in my PostGIS database using data from Geofabrik. The command is

osmosis -q --read-replication-interval workingDirectory=$HOME/maps/replication --write-pgsql-change database=osm

and the configuration file is

# -*- default-generic -*-

# The URL of the directory containing change files.
baseUrl=http://download.geofabrik.de/europe/great-britain-updates/

# Defines the maximum time interval in seconds to download in a single invocation.
# Setting to 0 disables this feature.
#maxInterval = 0
maxInterval = 86400

(I had to set maxInterval early on, to take only one update at a time, but now even setting it to 100 isn't helping).

This has worked very nicely for the last few years, but recently it has started failing with

org.springframework.dao.DuplicateKeyException: PreparedStatementCallback; SQL [INSERT INTO actions(data_type, action, id) VALUES(?, ?, ?)]; ERROR: duplicate key value violates unique constraint "pk_actions"
  Detail: Key (data_type, id)=(N, 469786539) already exists.; nested exception is org.postgresql.util.PSQLException: ERROR: duplicate key value violates unique constraint "pk_actions"
  Detail: Key (data_type, id)=(N, 469786539) already exists.

It's as if items are being thrown into actions but without taking account of the version numbers or something. When I connect using the psql client, the actions table is empty, so it's not a matter of stale data causing the problem.

If it helps, my state.txt now has

#Fri Feb 03 05:31:32 UTC 2017
sequenceNumber=1415
timestamp=2017-02-01T21\:21\:02Z

How can I get my database updating again?