TypeError: Cannot read property 'userId' of null while using Streamy.sessionsForUsers()

[2gen]

While using Streamy.sessionsForUsers(arrOfUserIds).emit('private', { body: 'This is a private message' }); we are getting sporadic errors in the server console that do not make sense:

Exception in callback of async function: TypeError: Cannot read property 'userId' of null
     at packages\yuukan_streamy.js:546:47
     at packages\underscore.js:234:20
     at _.each._.forEach (packages\underscore.js:147:22)
     at Function._.filter._.select (packages\underscore.js:233:5)
     at Object.Streamy.socketsForUsers (packages\yuukan_streamy.js:545:21)
     at packages\yuukan_streamy.js:690:24
     at runWithEnvironment (packages\meteor.js:1180:24)
     at Object.<anonymous> (packages\meteor.js:1193:14)
     at [object Object].onMessage (packages\yuukan_streamy.js:627:18)
     at packages/ddp-server/livedata_server.js:559:43

The user(s) that we are trying to emit to are online and haven't disconnected. And if we wait a little bit (less then a minute) the TypeError's in the server console stop and the connection is established again and messages are sent/received successfully.

The problem is the clients are missing out on important emits during their "blip".

Any ideas here?