Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
I was getting an issue with the Sling channel not connecting (while all others were connecting fine), and it was coming back with Error 12-23 saying it could not connect to the authentication service or it would just sit there forever on the Sling splash screen with the spinning wait cursor. In addition I was finding that I was unable to login into Sling.com from any of my computers and it would show a "Attention Required! | Cloudflare" captcha page, but then after I logged in, it would just repeatedly take me back to the login page. We also noticed a similar redirection that was happening for various (but not all) https web sites.
I was able to figure out that removing the wireless router from the network path by connecting direct to the cable modem resolved the issue, so this narrowed the problem down to the router.
I went into the router and noticed there was a firmware update available. After applying this, it still exhibited the same behavior, but I noticed there were some settings that needed to be re-applied. Once I reconfigured the router and saved the settings, everything started working for both the computers and the Roku devices.
I wanted to share this here in case it proved helpful to other's situation as it was a very frustrating 24 hours without things working correctly here. Hopefully this will save someone else from that same frustration.