For the past two days, on two separate domains around the same time each day, our nameserver has been changed to the GoDaddy default nameserver.
I’ve contacted GoDaddy and they’ve stated nothing has happened on their end I’ve checked the audit log for both accounts and there isn’t any suspicious activity.
Cloudflare is not your registrar, right? If so, Cloudflare cannot change your nameservers and you do need to contact your registrar for that. Your domain might have expired and your registrar changed that.