I know you said you ran a check switch, but to randomly loose ONE of your LNB's, it sounds like it has to be the switch. For the multi dish solution, did they post a single LNB running into the switch on your other dish, or was a DPP? If you have two DPP's, the switches will compete and you can randomly loose signal that way. Also, double check individual transponders, and ensure your cables from your seperator/triplexer behind your reciever are of equal length, as seperators can get funny from uneven or unduely long stretches of wire. also double check that you don't have any low freq barrels in the line and are on all RG6 (RG59 on anything except your backfeed will sometimes conduct the signal, sometimes impede it with no rhyme or reason.)
hopefully the new reciever fixed it though! If not, double check those possibilities.