PowerPivot "Process" models are not deleted from the SSAS PowerPivot instance on SharePoint by PYTrivedi10

We have an issue with the PowerPivot instance where the data refresh models being created are not deleted.

In addition to this, there are intermittent PowerPivot service disruptions that make it unavailable.

Here are the details:

Here are the high level details of the PowerPivot services hosted in our production farm currently:

Number of PowerPivot Models: 64+
Current Size of all PowerPivot models: 1.5GB+
Total DBs Created: 230+
Total Size of all DBs in PowerPivot instance of Analysis Service: 6GB+
Total Users hitting the servers on a day: 1500 +

Following are the issues in specific that we are observing:
1.     PowerPivot service connectivity stops intermittently on the environment.
a.     The memory consumption in the PowerPivot server is ~45GB (144GB available)
b.     The CPU consumption is pretty low
c.     The PowerPivot Analysis service can be connected directly (ServerName/PowerPivot) but not through SharePoint (http://ServerName/.../Filename.xlsx)

2.     PowerPivot service takes a lot of time to come up.
a.     From the symptoms it seems to be some issue with the creating new connections to PowerPivot. An IISRESET or App Pool recycle for the PowerPivot app Pool is generally what we do to resolve this issue.
b.     After an IISRESET is done, it takes about 40 – 60 min for PowerPivot to be up again. We are not sure why this takes so much time

3.     Identifying PowerPivot Thresholds / cause of PowerPivot failures
a.     We want to identify the threshold that PowerPivot is able to handle on our environment and how we can increase it. The primary aim being to ensure the service is available at all times.
b.     We tried the scale out option for PowerPivot but that did not work out as we could not set a PowerPivot file to refresh on both servers

4.     Multiple databases being created by PowerPivot on Analysis services.
a.     We have observed that for one PowerPivot model, there is 1 Sandbox cube and many Process cubes created. We are not sure how the multiple Process cubes impact/help in PowerPivot execution
b.     This creates also a bit of memory problem as well