You can use two SWM-32 cascaded together, instead of the four SWM-16. Either are going to do the same thing but having the SWM-32 (which can be directly cascaded together) is a lot less mess, with less points of failure.
[Link: solidsignal.com]

As far as the problem you are having. Intermittent issues like that are a nightmare on a system that size. It could be a problem with the LNB, distribution equipment, connections, etc.
Changing the LNB, putting in the two SWM-32, and redoing all connections at the headend - would go a long way to eliminating what could be causing the issue. But would cost a good budget. Otherwise you could be troubleshooting things for months.

Or as suggested above, install power controllers to auto reboot the system ever week or few days. To keep the system up and running. But that is going to cost a lot of budget too. And if the component(s) that are causing the problem get worse....