Too many variables. Is the Load Balancer record ? If so the only change that has been made is Cloudflare is returning DNS records from a LB pool and it seems unlikely LB would have any impact on perf as DNS is DNS.
If your site is and it is slow through Cloudflare, troubleshoot that… There’s nothing which indicates that is a LB related issue. But additional data would be required if you want anyone in the forum to help… like a link to the host/domain while it is running through Cloudflare.