Mobile Push Notifications Delayed for Days

Description:

Push notifications from RocketChat are delayed by a day or more. This causes confusion for our users and also wastes time in checking messages that have already been addressed day(s) before.

Steps to reproduce:

1. Send a message from user A to user B

Expected behavior:

An instant push notification in mobile phone if the user is not on the desktop or web app and already saw the message.

Actual behavior:

The push notification comes after a day or more.

Server Setup Information:

• Version of Rocket.Chat Server: 3.5.1
• Operating System: Ubuntu 18.04 LTS
• Deployment Method: Digital Ocean Image
• Number of Running Instances: 1
• DB Replicaset Oplog: ?
• NodeJS Version: CLI says 8.17.0, RocketChat Administration says 12.16.1
• MongoDB Version: 4.0.3

Client Setup Information

• Desktop App or Browser Version: Both
• Operating System: Android/iPhone

Additional context

I have heard this from multiple users and can replicate the issue myself. The notifications are sporadic and unreliable.

Relevant logs:

Not sure which logs are relevant here. Please inform me and I'll add them.

Start by reproducing the delayed notification with the listed Rocket.Chat, Node.js, MongoDB, Android, and iPhone setup, then determine which notification logs are relevant. Done means a user who is not active on desktop or web receives the push notification promptly and reliably after a message is sent.