Describe the bug
For some reason error() handler of my query gets called twice, once as an Error and the 2nd time as a GraphQLError. The query results definitely aren't in a cache or anything, so why does this happen?

To Reproduce
Nothing special, the query is registered like this:

apollo: {
        failingQuery: {
            query: failingQuery,
            error(err) {
                alert(err.message);
            }
        }
    },

And the alert is invoked twice.

Expected behavior
The handler should be called once, why would it be called twice?

Versions
vue: 2.6.11
@vue/apollo-option: 4.0.0-alpha.11 and also 3.x
apollo-client: 3.3.6

Additional context
No special setup is done here, it's a basic query that hasn't been cached