Greetings everyone. I've been dealing with this annoyance for two years. I've been in contact with the support staff for the application, and have tried everything suggested, but the issue still stands.
The application is League of Legends. The issue is when the game tries to launch lolclient.exe, I get this error: "Unable to connect to the server. If you have a firewall, it may be blocking the connection. Please refer to your firewall's documentation. Would you like to retry the connection?"
If I click "Retry," I'm stuck on a black screen for ~30 seconds and then it loads successfully. Sometimes it waits for ~30 seconds, prompts the error again, and then it's successful. It always eventually succeeds, but it takes a while to get there. Besides using a VPN and replacing hardware, I've tried literally everything suggested by the community and the staff. All necessary ports are forwarded and confirmed as open. I do not experience any persistent network issues besides this one.
I know that it's not actually related to my firewall for two reasons: 1. it happens on ANY computer on the network, regardless of software. If I use the computer on another network, it connects immediately, and 2. I've completely uninstalled my firewall software, disabled Windows Defender, and ensured that all firewall-related services were stopped. The router's internal firewall is disabled. The interesting thing is that the error does not prompt without firewall software running, BUT it still takes ~45 seconds to connect to the server.
I've discovered a workaround to this problem, and the reason it works makes no sense to me. If I could contact someone with networking experience and knowledge, I believe they may be able to use this information to diagnose the issue. What I must do is set AVG Firewall to "interactive mode." When the application asks for permission to access the internet, I manually allow it, unchecking the box to remember the rule. Then, the game connects immediately, with no issue. If I forget to uncheck the box (this may be an issue with AVG), deleting the rule will not restore this functionality. It will automatically allow the application until a new build of the client is released. Automatically allowing the application still results in an error, but manually allowing it every time allows it to work as intended.
If this issue is clearly independent of firewall software (unless the router's GUI lies to me and there actually is some secret firewall hiding somewhere), why can I use firewall settings to circumvent it? It seems as though the server cannot receive a response from me unless I actively send it. But I'm clueless about networking. I really don't know anything.
It could be that my modem/router/whatever is faulty. It is an old piece. However, I have no further issues with it and don't feel a particular need to replace it. I'd rather not throw money at a problem unless I know the "why." So that brings me here. Hopefully someone can help me out. I'm willing to provide any information necessary. The router is Westell A90-750015-07 and my ISP is Verizon DSL. It's irrelevant for me to post system specifications, as this occurs on a great variety of rigs, regardless of OS, software, or hardware.
As a final note, I wondered today if a firmware upgrade coincided with the dawning of this issue. I'm using the latest firmware, which was published god knows when. However, Westell's website does not list changelogs, nor release dates for firmware updates, so it's difficult for me to figure this out. I even went as far to check the Wayback Machine for archived copies of the webpage. The latest release is 3 releases after the newest in Dec. 2011. That's when the archives stop, so I can't look further. I began playing the game around March 2012, and started experiencing this issue in July 2012. It's been happening ever since.