It’s working fine here for me.
If it was twitch then every streamer using OBS would be complaining, as OBS iirc is FFMPEG under the hood.
You can also try the more basic FFMPEG test signal:
ffmpeg -re \
-f lavfi -i testsrc2=size=960x540 \
-f lavfi -i aevalsrc="sin(0*2*PI*t)" \
-vcodec libx264 \
-r 30 -g 30 \
-preset fast -vb 3000k -pix_fmt rgb24 \
-pix_fmt yuv420p \
-f flv \
rtmp://live-fra.twitch.tv/app/STREAMKEY
To exclude your source file being weird.
This paticular command is working correctly here on a server in Canada to the French injest. (Old command from my French server that I never updated to a nearer injest)