Jagged geometry after OSM update with Osmosis and Osm2pgsql

In my previous question https://help.openstreetmap.org/questions/66092, I asked for help concerning why edited features were missing after applying a daily changefile to my OSM postgis dataset. It was determined that I used the flat nodes option upon initial planet.pbf import to postgres (--flat-nodes D:\nodes.cache), and this option was also required in the osm2pgsql --append command.

I was able to successfully append a daily changefile to my database using the flat nodes option in the append command. However, after viewing the data through a localhost Geoserver service, all of the database geometry is corrupted. Specifically, what were once smooth curves in the osm_line layer are now jagged and blocky. Polygons are incorrectly shaped as well. Rectangular building footprints are now often triangular. It looks like some sort of generalization process is happening to the nodes.

Graphical examples:

Lines - https://imgur.com/YJeDrMg
Red is the original linework (before the append command). Thin purple is what the osm_line layer looks like after the append command.

Polygons - https://imgur.com/fXtftjk
Blue is the original linework (before append). Thin blue is what osm_polygon looks like after the append command.

Here are my commands used:

1) Initial planet import
osm2pgsql -c -d planet -U postgres -W -H localhost -S default.style c:\osm\planet.pbf -E 4326 -C 8000 -s --flat-nodes D:\osm_updates\nodes.cache --number-processes 6

2) Osmosis pull changefile based on local db state id
osmosis --read-replication-interval workingDirectory=d:\osm_updates --simplify-change --write-xml-change d:\osm_updates\changes.osc.gz

3) Osm2pgql append changefile to local postgres db
osm2pgsql --append d:\osm_updates\changes.osc.gz -d planet -U postgres -S default.style -E 4326 -C 8000 --slim --flat-nodes d:\osm_updates\nodes.cache --number-processes 6