The response time graphs changed substantially on a certain date.
While our monitoring system utilizes multiple nodes in disparate locations to confirm detected failures (primarily to avoid false alarms) the graphs are produced from a single node, and hence subject to this variability.
On the date in question, your host was re-allocated to a primary monitoring node in a different geographic location, hence the structural shift in the response time profile.
Such re-allocations are necessary from time to time to ensure the ongoing robustness of our monitoring system in all conditions.
Note that you can also specify your primary monitoring node for a given host.
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