Intermittent WebSocket alert

[stroomdev66]

When left for a while Stroom will sometimes show an error popup with the message: Error on web socket trying to keep application instance alive

and detail:

Error on web socket at wss://stroom-pki-zta-lb-alb-190028314.eu-west-2.elb.amazonaws.com/web-socket/application-instance
Unknown reason (code: undefined)

This is probably because the WS is closed frequently by the ALB and the attempt to send the keep alive message happens at a time when the WS is closed before it reopens.