For anyone experiencing issues connecting to pools, this info might help...
If, in your house you happen to own an ASUS wifi router/firewall, check and see if your model has a feature called 'Two-Way IPS' - which is part of the firewall and packet filtering settings and if you do, try disabling it.
I run an ASUS GT-AX11000 Router - one of their high end gaming routers and evidently the 'Two-Way IPS' logic inside the router was blocking the connection to slushpool. Of course there was NOTHING in the firewall's network protection dashboard that indicated this to be the case, but as soon as I disabled 'two-way IPS' the miner worked.
The background on this is as follows... I was pulling my hair out for two weeks or more trying to understand why I couldn't connect to any pool and then tried testing it using a VPN and discovered the connections were successful if using a VPN.
Since I knew that running the miner inside a VPN tunnel works, the question is, what is not 'seeing' the traffic due to the VPN? - Well, Comcast isn't seeing it, that's true and my ISP was what I was afraid was causing the issue. But with the VPN in use, the port filtering on my firewall/router ALSO isn't seeing traffic to e.g. slushpool, and that's why subsequent connection attempts worked. Turns out it wasn't Comcast, it was my firewall.
Turns out other miners also have experienced this issue. Check this old post on Reddit:
https://www.reddit.com/r/MoneroMining/comments/m1g0y1/cannot_reach_any_pool_without_tls/