Problem with Proxy Access for Some Users

Hello everyone! I’m facing an issue with my proxy configuration. I have an endpoint set up for proxy, such as api.domain.com. When the proxy is enabled, some users are unable to access the Cloudflare server. However, when these same users access the Load Balancer directly, the connection works fine. The problem occurs only for specific users, and it's not a widespread issue. Additionally, when running a curl -v telnet://api.domain.com:443 to test the connection, the same users encounter the error mentioned. It’s worth noting that when the proxy is disabled, the connection is successful. Interestingly, when users are using a VPN or Cloudflare Warp connection, the proxy connection works fine. What I’ve tried so far: I’ve checked the proxy configurations but couldn’t find anything explaining this behavior. I’ve tested with different users and different networks (with/without VPN). Our hypothesis is that there might be some Cloudflare block for a particular route or ISP, preventing the TCP connection on port 443 for the proxy IPs. The same test on other domains with different proxy IPs works fine. What I need: Has anyone encountered something similar? Any suggestions on how to investigate this further or resolve the intermittent access issue? Thanks in advance for your help!