You may have a Page Rule or something on your server that redirects that subdirectory from www to the root domain. Your main site loads as www.
What did you install in that subdirectory?
When I try that subdirectory, the error I get is: ERR_SSL_VERSION_OR_CIPHER_MISMATCH
So…www goes direct to your server which has Let’s Encrypt installed, but non-www goes through Cloudflare and it does not have SSL properly configured.
You need to decide if you want to proxy through Cloudflare, or not. And if you want to use Cloudflare, make sure you have SSL properly set up.