OpenStreetMap instance is unusable with latest planet, but works with last year PBF

I'm running a custom OpenStreetMap instance on my server, with both the standard openstreetmap-carto style and a custom style. The current version up and running in production uses a planet file from 2019-09-12.

I now want to update the data from the latest planet file on my dev server.

I have a script that will:

• download the latest file
• tune the database for the import
• drop and recreate the database
• import the PBF
• create the indexes
• tune the database for production use

The server is a quad-core i7-6700 with 64 GB of RAM, a 1 To SSD (storing the database) and 8 TB of hard drives (storing the tiles).

Here's the script code:

# Define some values:
PBF=~/data/planet-latest.osm.pbf
THREADS=8
CORES=4

# Download latest PBF:
wget https://planet.openstreetmap.org/pbf/planet-latest.osm.pbf -O $PBF

# Drop the databse:
sudo -u postgres dropdb osm

# Recreate the databse:
sudo mkdir -p /ssd/db/osm
sudo chown postgres /ssd/db/osm
sudo -u postgres psql -c "CREATE TABLESPACE osm_tablespace LOCATION '/ssd/db/osm';"
sudo -u postgres createdb -E UTF8 -O myusername -D osm_tablespace osm

# Setup PostGIS:
sudo -u postgres psql osm -c "CREATE EXTENSION postgis;"
sudo -u postgres psql osm -c "CREATE EXTENSION hstore;"
sudo -u postgres psql osm -c "ALTER TABLE geography_columns OWNER TO myusername;"
sudo -u postgres psql osm -c "ALTER TABLE geometry_columns OWNER TO myusername;"
sudo -u postgres psql osm -c "ALTER TABLE raster_columns OWNER TO myusername;"
sudo -u postgres psql osm -c "ALTER TABLE raster_overviews OWNER TO myusername;"
sudo -u postgres psql osm -c "ALTER TABLE spatial_ref_sys OWNER TO myusername;"

# Fine tune for import
if [ ! -f /etc/postgresql/10/main/postgresql.conf.bak ]; then
    sudo cp /etc/postgresql/10/main/postgresql.conf /etc/postgresql/10/main/postgresql.conf.bak
fi

sudo rm /etc/postgresql/10/main/postgresql.conf
sudo cp /etc/postgresql/10/main/postgresql.conf.bak /etc/postgresql/10/main/postgresql.conf

sudo tee -a /etc/postgresql/10/main/postgresql.conf << EOF
synchronous_commit = off        # /!\ Use these for OSM import only
fsync = off                     # /!\ Use these for OSM import only
random_page_cost = 1.1
wal_buffers = 16MB
effective_cache_size = 48GB
maintenance_work_mem = 8GB
shared_buffers = 16GB
work_mem = 4GB
autovacuum = on
effective_io_concurrency = 200
max_connections = 300
checkpoint_completion_target = 0.7
default_statistics_target = 100
min_wal_size = 1GB
max_wal_size = 4GB
max_worker_processes = $THREADS
max_parallel_workers_per_gather = $CORES
max_parallel_workers = $THREADS
EOF

sudo service postgresql restart

# Import the PBF:
mkdir -p /ssd/flat-nodes

osm2pgsql \
    -d osm \
    --create --slim --multi-geometry --hstore --drop \
    --cache 20000 \
    --number-processes 1 \
    --tag-transform-script ~/src/map-styles/openstreetmap-carto/openstreetmap-carto.lua \
    --style ~/src/map-styles/openstreetmap-carto/openstreetmap-carto.style \
    --flat-nodes /ssd/flat-nodes/osm.cache \
    "$PBF"

# Create the indexes:
cd ~/src/map-styles/openstreetmap-carto
psql -d osm -f indexes.sql

# Fine tune for production:
sudo rm /etc/postgresql/10/main/postgresql.conf
sudo cp /etc/postgresql/10/main/postgresql.conf.bak /etc/postgresql/10/main/postgresql.conf

sudo tee -a /etc/postgresql/10/main/postgresql.conf << EOF
#synchronous_commit = off        # /!\ Use these for OSM import only
#fsync = off                     # /!\ Use these for OSM import only
random_page_cost = 1.1
wal_buffers = 16MB
effective_cache_size = 48GB
maintenance_work_mem = 8GB
shared_buffers = 16GB
work_mem = 1GB
autovacuum = on
effective_io_concurrency = 200
max_connections = 300
checkpoint_completion_target = 0.7
default_statistics_target = 100
min_wal_size = 1GB
max_wal_size = 4GB
max_worker_processes = $THREADS
max_parallel_workers_per_gather = $CORES
max_parallel_workers = $THREADS
EOF

I have already successfully used that script in the past. But if I run it now, my map becomes super slow (with both openstreetmap-carto style and mine), like if it was missing all the indexes. Running the script on the 2019-09-12 PBF results in a perfectly usable map.

What could be wrong? Did the OSM database schema change since last year? Do I need to delete the flat-nodes files before importing again?

Thanks in advance