Multiple instances running on same server interfere with each other

Situation is this;

I have two instances of Nextcloud running on the same physical server on different domain names.
These two instances use a different redis database/index/prefix (or whatever you would like to call it, the dbindex parameter).
I have also set up two instances of notify_push listening on different ports on the same server.

Startup trace on the first instance;

[2021-09-09 10:37:54.083333 -04:00] TRACE [notify_push] src/main.rs:46: Running with config: Config { database: AnyConnectOptions(MySql(MySqlConnectOptions { host: "localhost", port: 3306, socket: None, username: "----", password: Some("----"), database: Some("nc1"), ssl_mode: Preferred, ssl_ca: None, statement_cache_capacity: 100, charset: "utf8mb4", collation: None, log_settings: LogSettings { statements_level: Info, slow_statements_level: Warn, slow_statements_duration: 1s } })), database_prefix: "oc_", redis: [ConnectionInfo { addr: Tcp("127.0.0.1", 6379), redis: RedisConnectionInfo { db: 0, username: None, password: None } }], nextcloud_url: "https://nc1.my.tld/", metrics_bind: None, log_level: "notify_push=trace", bind: Tcp(0.0.0.0:7867), allow_self_signed: false, no_ansi: false }
[2021-09-09 10:37:54.086174 -04:00] DEBUG [notify_push::storage_mapping] src/storage_mapping.rs:96: querying storage mapping for 1
[2021-09-09 10:37:54.154635 -04:00] TRACE [notify_push] src/main.rs:63: Listening on 0.0.0.0:7867

Startup trace on the second instance;

[2021-09-09 10:35:48.107783 -04:00] TRACE [notify_push] src/main.rs:46: Running with config: Config { database: AnyConnectOptions(MySql(MySqlConnectOptions { host: "localhost", port: 3306, socket: None, username: "----", password: Some("----"), database: Some("nc2"), ssl_mode: Preferred, ssl_ca: None, statement_cache_capacity: 100, charset: "utf8mb4", collation: None, log_settings: LogSettings { statements_level: Info, slow_statements_level: Warn, slow_statements_duration: 1s } })), database_prefix: "oc_", redis: [ConnectionInfo { addr: Tcp("127.0.0.1", 6379), redis: RedisConnectionInfo { db: 2, username: None, password: None } }], nextcloud_url: "https://nc2.different.tld/", metrics_bind: None, log_level: "notify_push=trace", bind: Tcp(0.0.0.0:7869), allow_self_signed: false, no_ansi: false }
[2021-09-09 10:35:48.111389 -04:00] DEBUG [notify_push::storage_mapping] src/storage_mapping.rs:96: querying storage mapping for 1
[2021-09-09 10:35:48.386990 -04:00] TRACE [notify_push] src/main.rs:63: Listening on 0.0.0.0:7869

As you can see, instances are listening on different ports, connecting to different nextcloud instances, and using different redis db's.

Apache config, INST 1:

        ProxyPass /push/ws ws://localhost:7867/ws
        ProxyPass /push/ http://localhost:7867/
        ProxyPassReverse /push/ http://localhost:7867/

Apache config, INST 2:

        ProxyPass /push/ws ws://localhost:7869/ws
        ProxyPass /push/ http://localhost:7869/
        ProxyPassReverse /push/ http://localhost:7869/

When a client connects, it connects to the correct instance of notify_push, and it proceeds to regularly ping the users connected to that instance.

The PROBLEM, however, is that when a message is generated by EITHER instance of Nextcloud, it ends up being received by BOTH instances of notify_push. This is especially a problem when there is username overlap between the two Nextcloud instances, because when a notification is meant for {username}/nc1, it is delivered to both {username}/nc1 and {username}/nc2.

Start with the Redis-related code under src/ and the startup and storage-mapping entry points mentioned in src/main.rs and src/storage_mapping.rs. Reproduce two notify_push instances using the separate Redis database indexes from the report, then trace how messages are published and received. Done means a notification from one Nextcloud instance is not delivered by the other instance.