Duplicate key error when trying to log in with GitHub connected account after recent database migration

Description:

It looks like snap triggered a database migration (but not an application update) on our chat server this morning:

I found that I had been automatically logged out this morning, most likely because of this migration. I had been logged in via OAuth with my connected Github account. When I try to log back in with the same account using the Github integration, I get a generic "Internal server error" message.

When I check the logs using a separate, non-OAuth account, I can see this error being generated when I try to log in:

Exception while invoking method 'login' MongoError: E11000 duplicate key error collection: parties.users index: services.github.id_1 dup key: { : 5004534 }     at Function.MongoError.create (/snap/rocketchat-server/1273/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb-core/lib/error.js:31:11)     at toError (/snap/rocketchat-server/1273/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/utils.js:139:22)     at /snap/rocketchat-server/1273/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/collection.js:1059:67     at /snap/rocketchat-server/1273/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb-core/lib/connection/pool.js:469:18     at _combinedTickCallback (internal/process/next_tick.js:131:7)     at process._tickDomainCallback (internal/process/next_tick.js:218:9)

It appears that it is trying to create a duplicate record on a unique key - is it trying to recreate the record for my OAuth account, instead of finding the one that already exists?

Server Setup Information:

• Version of Rocket.Chat Server: 0.65.1
• Operating System: Ubuntu
• Deployment Method: snap
• Number of Running Instances: 1
• DB Replicaset Oplog: Enabled
• NodeJS Version: v8.11.2

The reported entry point is the login method for the GitHub integration; start by tracing how the existing services.github.id_1 MongoDB unique index is handled during OAuth login. Reproduce the failure on Rocket.Chat 0.65.1 with the listed snap/Ubuntu setup and verify that an already connected account can log in without the duplicate-key error.