Subscriptions fails with untraceable error

[gpsamson]

I've been trying to trace a subscription_failed error for hours without any success. The data sent to the client on failure is {"type":"subscription_fail","id":0,"payload":{"errors":[{"message":"Cannot read property 'forEach' of undefined"}]}}.

There is nothing logged to the console of the server. I've also checked the application code and there is no use of forEach so I suspect it's rooted in graphql-subscriptions or subscriptions-transport-ws. Both the client and server are using the latest releases of the Apollo stack.

Subscriptions were working flawlessly up until I resumed development today. I'm going to check out the master branch and see if it the error is still happening. I'll also attempt a clean install.

I couldn't find an issue similar to this one so I'm opening this in hope of some direction. Any help is much appreciated.

[gpsamson]

Fixed - An incorrect GQL query on the client side was making the subscription manager throw this vague error.