The other site was also on cloudflare but didn’t have caching enabled. The new site root has aggressive caching enabled via page rules, which would also apply to subfolders, hence the issue.
Browser Cache TTL: a month, Always Online: On, Cache Level: Cache Everything, Edge Cache TTL: 2419200 seconds
I also think following header is also critical.
proxy_set_header X-Forwarded-Proto https;