You probably had both 2,4 and 5 GHz networks separated - but by connecting Helix Pods, the band steering feature (same access points name for both) is automatically switched on and you cannot disable it. That is why you can only see the 2,4 GHz name, 5 GHz is bearing the same name but you can't see it because they are unified. Regarding the speed drop, that can happen, but usually not at such rate.
We will need more information by accessing your Videotron account; please follow up by phone/chat/Facebook/Twitter for advanced troubleshooting. Thank you -Berenger