I have an idea. I have seen this issue before on my Wally, connected to a DPP44 switch. Sometimes the only way to fix this is to "reset" the switch. First, unplug the power inserter. Then, just to make sure that there is not a separate issue with the Wally, disconnect the coax from the back of the Wally, and run the Test Installation. The test will fail, obviously. This test is just to clear any old settings out of the Wally's memory. Then, reconnect the coax, plug in the power inserter, and run the Test Installation again. If your switch and power inserter are still working properly, and all cables are still securely connected, then this procedure should fix the problem.
I will note that when I saw this issue (which only happened rarely) it would usually be after the nightly reset, when I turned on the Wally for the first time that day. So, I am not sure what would cause it to happen while you were in the middle of watching TV. The steps above are one thing you can try in order to either fix the issue or diagnose what is happening. If those steps do not help, then disconnect the switch outside. Use barrel connectors to connect the cables coming from the dish to the cables that were connected to ports 2, 3, and 4 on the switch. This ensures that the power inserter is no longer in the system, since that would be connected to port 1. After doing that, you will need to do the Test Installation on the other three Wally receivers. The Wally connected through your power inserter will no longer be hooked up to the dish. This should restore signal to those three receivers. If that does not work, then there is a problem with either: the LNB, the alignment of the dish, or possibly some damaged cables.