Entries do not sync if there are no more entries on the server but there still are entries in the app

[Shocker]

Environment

• Version: 2.6.5 (6b7e9ec1df4235ce77cad3f36055dad59151dbaf)
• Installation: git clone + make install
• PHP version: 7.4
• OS: Ubuntu 20.04
• Database: MySQL 5.7.40

My app/config/parameters.yml is:

# This file is auto-generated during the composer install
parameters:
  database_driver: pdo_mysql
  database_host: ***
  database_port: ***
  database_name: ***
  database_user: ***
  database_password: ***
  database_path: null
  database_table_prefix: ***
  database_socket: null
  database_charset: utf8mb4
  domain_name: '***'
  server_name: Wallabag
  mailer_dsn: '***'
  locale: en
  secret: ***
  twofactor_sender: ***
  fosuser_registration: false
  fosuser_confirmation: false
  fos_oauth_server_access_token_lifetime: 3600
  fos_oauth_server_refresh_token_lifetime: 1209600
  from_email: ***
  rss_limit: 50
  rabbitmq_host: ***
  rabbitmq_port: ***
  rabbitmq_user: guest
  rabbitmq_password: guest
  rabbitmq_prefetch_count: 10
  redis_scheme: tcp
  redis_host: ***
  redis_port: ***
  redis_path: null
  redis_password: null
  sentry_dsn: null

What steps will reproduce the bug?

1. Start a fresh install, empty entries database
2. Add some entries from the web or API
3. Go to phone app, sync. The entries will appear correctly
4. Delete ALL entries from the web or API
5. Go to phone app, sync. The entries will NOT disappear
6. Add 1 entry from the web or API
7. Go to phone app, sync. The new entry will appear
8. Sync one more time, the old entries will correctly disappear