The problem is related to defect # DE348055 and it affects any 10.x release
The root cause of the issue are remaining metrics data that are not cleared from the subscription list once the agent is unmounted. The tracked metrics in graph still contains the data that are being refreshed only until the agent is unmounted, so after the agent is automatically unmounted (by default 1 hour) the time frame (x-axis) starts expanding with every refresh and since we only have graph values for the last 8 minutes the graph itself looks like it is collapsing.
This issue is fixed in 10.7.0 SP1 and 10.5.2 HOTFIX#39
Reopen the dashboard
NOTE: To obtain a copy of the HOTFIX contact CA Support.