Since I am also getting this issue, I think it would be ok if I responded for him, as this has become a chronic issue for me. The message is "Disconnected for spamming." It happens sometimes even as I am typing the command if it is long enough. (ie 20+ characters.) if it doesn't kick me for typing it all out, it usually does for entering it. I've been getting this problem a ton on Minehut.com as well as other places. I'm not sure if it is a Minehut-only problem or not since they are running protocol hacks and the like, but I think it would be something to check from a dev point of view. Also, typing in books messes me up as well.
This problem still persists, as well as it putting a t in chat quite often when I type. Bumping this in the hope it gets fixed soon. - Running 1.15.2 btw.