Your CPU isn't powerful enough to run the game and encode 1920x1080@60fps with x264 at the same time. Switch the encoder from x264 to nvenc and limit the game to 60 fps by activating vsync or some other fps limiter.
Second problem, to be resolved once you get a stream without lost frames: you're trying to stream this resolution with a bitrate of 2500. This isn't even remotely enough bitrate to get decent video quality. See here the Twitch broadcasting guidelines:
https://stream.twitch.tv/encoding/
As long as you aren't partnered with Twitch, it is recommended to stream with 720p instead of 1080p, since Twitch doesn't recode and produce downscaled streams for non-partnered streams. The bandwidth requirement for 720p is lower.
