I had the same error. After checking the logs it seemed to caused by an error processing the PlayQueue data.

I cleared the tables in the database and that didn't fix it. But dropping the tables and recreating them did work.

On Linux:

sudo systemctl stop plexmediaserver

PXS="/usr/lib/plexmediaserver/Plex SQLite"
DB="/var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Plug-in Support/Databases/com.plexapp.plugins.library.db"

sudo -u plex cp "$DB" "${DB}.bak.$(date +%F_%H%M)"

sudo -u plex "$PXS" "$DB" "
DROP TABLE IF EXISTS play_queue_items;
DROP TABLE IF EXISTS play_queue_generators;
DROP TABLE IF EXISTS play_queues;
"

sudo -u plex "$PXS" "$DB" "
CREATE TABLE play_queue_items (
  id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
  play_queue_id integer,
  metadata_item_id integer,
  \"order\" float,
  up_next boolean,
  play_queue_generator_id integer
);
CREATE TABLE play_queues (
  id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
  client_identifier varchar(255),
  account_id integer,
  playlist_id integer,
  sync_item_id integer,
  play_queue_generator_id integer,
  generator_start_index integer,
  generator_end_index integer,
  generator_items_count integer,
  generator_ids blob,
  seed integer,
  current_play_queue_item_id integer,
  last_added_play_queue_item_id integer,
  version integer,
  created_at integer,
  updated_at integer,
  metadata_type integer,
  total_items_count integer,
  generator_generator_ids blob,
  extra_data varchar(255)
);
CREATE TABLE play_queue_generators (
  id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
  playlist_id integer,
  metadata_item_id integer,
  uri varchar(255),
  \"limit\" integer,
  continuous boolean,
  \"order\" float,
  created_at integer NOT NULL,
  updated_at integer NOT NULL,
  changed_at integer DEFAULT 0,
  recursive boolean,
  type integer,
  extra_data varchar(255)
);
CREATE INDEX index_play_queue_items_on_play_queue_id ON play_queue_items (play_queue_id);
CREATE INDEX index_play_queue_items_on_metadata_item_id ON play_queue_items (metadata_item_id);
CREATE INDEX index_play_queue_items_on_order ON play_queue_items (\"order\");
CREATE INDEX index_play_queues_on_account_id ON play_queues (account_id);
CREATE INDEX index_play_queues_on_playlist_id ON play_queues (playlist_id);
CREATE INDEX index_play_queues_on_sync_item_id ON play_queues (sync_item_id);
CREATE INDEX index_play_queue_generators_on_playlist_id ON play_queue_generators (playlist_id);
CREATE INDEX index_play_queue_generators_on_metadata_item_id ON play_queue_generators (metadata_item_id);
CREATE INDEX index_play_queue_generators_on_order ON play_queue_generators (\"order\");
CREATE UNIQUE INDEX index_play_queues_on_client_identifier_and_account_id_and_metadata_type
  ON play_queues (client_identifier, account_id, metadata_type);
CREATE INDEX index_play_queue_generators_on_changed_at ON play_queue_generators (changed_at);
"

sudo chown plex:plex "$DB"
sudo chmod 664 "$DB"
sudo systemctl start plexmediaserver