Thanks for reaching out. What device are you on? Do you see this happening across devices/browsers? Also, do you see any specific error message when you try to comment? Let us know.
Thanks for trying those steps. Usually, your account getting a Copyright strike shouldn't affect your ability to comment on a video/live stream. Recommending you to send a feedback report directly from YouTube with these steps so that we can work on it: https://goo.gl/WdI0BK