Don't stream over Wifi. It's designed for lightweight mobile use, not as a replacement for running cables. It's very prone to disruption and interference, especially for minimum-constant-rate throughput crucial applications like livestreaming. In some cases USB adapters seem to cause 'bus jams' where the OS is stuck waiting for I/O, which can disrupt other processes.
You also really don't want to stream at 3500kbps unless you're a Partnered streamer. Many of your viewers will buffer. 720p@30fps, 2000kbps is the 'golden point' for non-partnered streams.
With how inexplicably CPU-heavy BF4 is, streaming at 60fps appears to be overwhelming your system; you're duplicating a bunch of frames as well, which suggests this too.