Can't help you on the first one other than possible NAT issues (strict or moderate) within the party that is causing delays. I occasionally have difficulty finding a round and just back out of my current lobby and reinitiate the search.
As to Swarm, I just don't run the higher lethal scorestreaks after getting the calling cards closed out. Nothing causes the other team to evaporate more quickly than calling one in and that may very well be what happened to you. Enemy Swarm inbound. Leave. Replace. What? There's already a Swarm I am leaving. Rinse, repeat.
Could have limited your kills with lobby turnover.
Can't say I have ever had the opposition leave on calling in an EMP or VSAT so I pretty much cap out at those as mentioned.