From the screenshot, it looks like Go-http-client is recognized as bot or HTTP DDoS.
Are you using some service or app which contains such user-agent?
It looks legit to be blocked since it’s not a real user. Could be I am wrong 
I am sorry to hear this.
Kindly, if you have received an email related to your zone having potentially abusive behaviour, please reply to the email that you’ve received from Cloudflare team.
Otherwise, please reach out directly to [email protected].
This issue has to be checked and solved by the Trust&Safety team.
Thank you for patience.
Please, do acknowledge below if it’s related to your case as well: