Yeah it is weird and it is not limited to silver only. What i do if my lobby is still empty after some minutes of waiting i start the match and try to solo or die as fast as possible either way people will come immediately after i get back to lobby or they will join game in progress.
There appears to have been some kind of undocumented alteration to the matchmaking on PC, that tries to fit you with people near your N7 rating. Thus players with an N7 outside the normal range for any given difficulty are having a crapton of trouble filling lobbies.
I have an n7 of approximately 1130 (don't remember and am on my phone atm) and am a pc player (UK timezone), I was having the same issue earlier to the point I couldn't get a full lobby for a couple hours that I just did a couple solo Silvers before I just meh'd, logged off and to minecraft. I also noticed that half the time I was joining games that had already begun (joining mostly after wave 3 instead of wave 1, sometimes even wage 6 :s ) kinda annoying at times specially when friends are offline and you have to pug it to play it.