Website becomes inaccessible without vpn

I'm experiencing an issue similar to the one in this thread:
https://community.cloudflare.com/t/web-site-wont-work-unless-i-use-a-vpn/241146/15.

I have four subdomains, each linked to a different server. One of them (X) is located in the US, while the other three are in Europe. All my websites are proxied through Cloudflare.

The problem is that server X often requires me to use a VPN to access my website. Without a VPN, it either times out or shows an "unreachable" error. However, when I access X directly without Cloudflare proxy, it works fine. Occasionally, X works without a VPN, but most of the time, I face this issue. However, the other 3 servers work most of the time fine, but also require vpn a few times in a week.
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