When creating a federation upstream, in the uri if connection_timeout amqp param is added it needs to be in milliseconds not seconds according to the documentation. This was found in 3.4.3.
Example
amqp://user:password@SERVER?heartbeat=10&connection_timeout=10
should be
amqp://user:password@SERVER?heartbeat=10&connection_timeout=10000
From https://github.com/rabbitmq/rabbitmq-server/issues/1015: