I had someone do that to me because they had some issues with my fictional content. They never communicated and later slandered me ^^; along with doing other illegal and questionable things.

I've never heard of someone getting banned over that thankfully, the ownership log acts as proof of who made designs and it's never your fault if someone chooses to remove their own credits from art/ designs on here.

I believe some people do it, so they don't feel associated to a user they don't like. Some people even get harassed on here as a result of leaving credits up to someone who their social group doesn't like and are pressured into removing them.

I'm sorry it happened to you :(  Luckily there's little chance of you actually getting banned over this.