Error during metric collection with 2 instances of a GAE service running

[mwohlin]

Collecting this metric (stackdriver_gae_app_appengine_googleapis_com_system_memory_usage) works fine as long as there is only 1 instance of the GAE service running. As soon as we scale to 2 instances running, StackDriver_Exporter begins to fail and throws the following error when accessing metrics at the /metrics url. I have changed the module_id and project_id to generic values before creating this post.

An error has occurred during metrics collection:

collected metric stackdriver_gae_app_appengine_googleapis_com_system_memory_usage label:<name:"module_id" value:"service-name" > label:<name:"project_id" value:"project-name" > label:<name:"unit" value:"By" > label:<name:"version_id" value:"v0-39-0" > gauge:<value:9.87049984e+08 >
was collected before with the same name and label values