Reset gauge on refresh

Author: skoeva

backend/pkg/metrics/metrics.go

@@ -156,6 +156,9 @@ func RegisterAndInstrument(api *api.API) error {
 
 // calculateMetrics calculates the application metrics and updates the respective metric.
 func calculateMetrics(api *api.API) error {
+	// reset instance stats on each refresh
+	latestInstanceStatsGaugeMetric.Reset()
+
 	aipcMetrics, err := api.GetAppInstancesPerChannelMetrics()
 	if err != nil {
 		return fmt.Errorf("failed to get app instances per channel metrics: %w", err)