[osm2pgsql] error during uploading changeset to nominatim

   /app/nominatim/build/osm2pgsql/osm2pgsql -klas --number-processes 1 -C 2000 -O gazetteer -d nominatim.nominatim -P 5432 -U n_user -H nominatim-pgpool-service.nominatim  /app/diff_53820819.osc

I got pgpool and 3 psql nodes. Periodically cron spawning a script to download changes from osm and upload them to nominatim.

During upload process I there is error:

osm2pgsql version 0.96.0 (64 bit id space)

Using projection SRS 4326 (Latlong)
Allocating memory for dense node cache
Allocating dense node cache in one big chunk
Allocating memory for sparse node cache
Sharing dense sparse
Node-cache: cache=2000MB, maxblocks=32000*65536, allocation method=11
Mid: pgsql, cache=2000
Setting up table: planet_osm_nodes
Setting up table: planet_osm_ways
Setting up table: planet_osm_rels

Reading in file: /app/diff_53820819.osc
Using XML parser.
node cache: stored: 0(-nan%), storage efficiency: -nan% (dense blocks: 0, sparse nodes: 0), hit rate: -nan%
Osm2pgsql failed due to ERROR: delete_rel failed: server closed the connection unexpectedly
    This probably means the server terminated abnormally
    before or while processing the request.
(7)
Arguments were: 80305167,
ERROR: Error from osm2pgsql, 1

In pg-pool logs:

2018-10-09 10:57:41 ERROR: pid 58: Bind: cannot get parse message "delete_rel"
2018-10-09 10:57:41 LOG:   pid 58: do_child: exits with status 1 due to error

2018-10-09 10:57:41 LOG:   pid 89: ProcessFrontendResponse: failed to read kind from frontend. frontend abnormally exited
2018-10-09 10:57:41 LOG:   pid 103: ProcessFrontendResponse: failed to read kind from frontend. frontend abnormally exited
2018-10-09 10:57:41 LOG:   pid 95: ProcessFrontendResponse: failed to read kind from frontend. frontend abnormally exited

As I understand "delete_rel" is a prepared statement which was not created. But when I tried to do the same operation locally it's working even without that prepared statement.

Any suggestions how to resolve this?