How to remove orphan push tokens?

We see many push tokens in the log as a queue, which could not be delivered and then hold back new push notifications. This is happening e.g. to users, who do not have an Android phone with Google services enabled, and then switch to another device with Google service enabled. They never get a push notifications, even after weeks.

[34mI20170424-16:09:06.164(2) Push: Could not send notification id: "MRQxxxxxxDyoe9PK", Error: Push.send got a faulty query
[34mI20170424-16:09:06.168(2) Push: Send message "user.test" via query { userId: 'fjCWxDLkbf8K95thD' }

As soon as we remove the tokens from "_raix_push_app_tokens" in the Mongo DB, the push notifications are successfully delivered.

We thought about removing all tokens in a cron job each night, but maybe there is a smarter solution? Or give the tokens a TTL.

Rocket.Chat Version: 0.52

Start by tracing the Push.send failure and the _raix_push_app_tokens MongoDB collection described in the report. Determine how undeliverable tokens are handled and define completion as preventing stale tokens from blocking later push notifications, with the behavior verified against the reported device-switch case.