You can see on the dashboard this kind of chart
This chart means that your proxy has filled 95% of it’s cache area (2GB by default).
This is not an issue
When reaching 95%, the proxy service must remove old stored objects that are not regulary requested in order to store new objects.
In fact, your proxy will decrease it’s cache rate because it cannot save more data on it’s local disk.
To increase storage capacity you can use the Cache control center in order to add new cache storage or to increase the main cache storage.