I had a look up about EE and found a few points...
1. Modern networks handle internet traffic differently. EE natively supports IPv6, which is the newest standard of internet routing. However, some website servers are misconfigured or incompatible with mobile IPv6 connections. Because your Vodafone SIM might use a different routing setup (e.g., sticking to IPv4), it successfully connects while your EE connection times out.
2. When you type in a URL, your phone connects to your network's Domain Name System (DNS) to locate the website. If EE's DNS server is having trouble resolving a specific website's domain or has cached outdated information, the site won't load.
3. EE applies varying traffic management policies based on your contract type, and network-level "content filters" (e.g., parental locks) might actively block certain sites or forums if they are categorized as restricted.
4. Mobile networks have distinct physical masts. What appears to be an issue with a specific site might just be a weak EE signal at that exact location. Your phone may struggle to complete the "handshake" to load a webpage if the data signal is too degraded.