user data export on multi-instance server does not work

Description:

My Data Download and Export Messages features do not work properly on multi-instance server.

Steps to reproduce:

1. Go to either 1) My Account > Preferences > My Data > Download My Data or 2) Room > Room Info > Export Messages (be sure to choose a room with adequate content)
2. You can have multiple users do this simultaneously to reach the max faster.
3. When the server reaches a limit, the rocketchat service will stop and the entire site crashes.
4. Restart the rocketchat service to bring the system back online.

Expected behavior:

The user should receive an email with a link to download a file containing:
My Data Download - all content from a user's account
Export Messages - all content selected from designated channel

Actual behavior:

The service crashes with no warning or the export/download goes into a permanent "exporting" status but never completes. We have been unable to find a way to get advance notice of a potential problem and have had to disable both features.

Server Setup Information:

• Version of Rocket.Chat Server: 3.6.0
• Operating System: Amazon Linux 2
• Deployment Method: tar
• Number of Running Instances: 3 instances on a single host
• DB Replicaset Oplog:
• NodeJS Version: v12.16.1
• MongoDB Version: 4.0.18

Client Setup Information

• Desktop App or Browser Version: Same on both
• Operating System:

Additional context

Relevant logs: