我有app-1部署，并为此配置了HPA。HPA似乎没有按预期工作，因为即使内存使用量（108%）超过目标，HPA也不会添加更多副本。

$ kubectl get hpa                               
NAME              REFERENCE                    TARGETS             MINPODS   MAXPODS   REPLICAS   AGE
app-1          Deployment/app-1                109%/100%, 5%/70%   2         4         3           3d

$ kubectl describe hpa app-1
...
Metrics:                                                  ( current / target )
  resource memory on pods  (as a percentage of request):  109% (5827813376) / 100%
  resource cpu on pods  (as a percentage of request):     18% (361m) / 70%
Min replicas:                                             2
Max replicas:                                             4
Behavior:
  Scale Up:
    Stabilization Window: 400 seconds
    Select Policy: Max
    Policies:
      - Type: Pods  Value: 1  Period: 60 seconds
  Scale Down:
    Stabilization Window: 400 seconds
    Select Policy: Min
    Policies:
      - Type: Pods  Value: 1  Period: 60 seconds
Deployment pods:    3 current / 3 desired
Conditions:
  Type            Status  Reason              Message
  ----            ------  ------              -------
  AbleToScale     True    ReadyForNewScale    recommended size matches current size
  ScalingActive   True    ValidMetricFound    the HPA was able to successfully calculate a replica count from memory resource utilization (percentage of request)
  ScalingLimited  False   DesiredWithinRange  the desired count is within the acceptable range
Events:           <none>

有人能帮我解释一下到底怎么了吗？