Ok, so you are connected to the 2.4 ghz network.
Now, for probably a more important issue. You mentioned you have a comcast dual band modem, that means you h ave comcast service. You know that comcast caps netflix streaming yes?
This has been going on since 2014. By cap, what that means is that after you stream X amount of data from netflix using comcast internet, they buffer your speed for netflix. This is almost certainly what is happening as you said yourself, youtube works fine. And I bet if you tested hulu, it would work fine too. ( for a while )
Im willing to bet if you take that wii to another location that has non comcast internet, netflix will stream fine. Or, if you have a phone capable of providing a wireless hotspot, netflix would even stream through the wireless hotspot from your mobile phone.
And at the beginning of your monthly billing cycle, netflix will work fine again. ( Till you hit the cap )
About the only fix you could do here is call comcast and ask t hem to remove the cap on netflix, or else you want to switch to a new provider. The first line customer service personell will probably either deny, or redirect the issue and claim its something else. It isnt.
A quick google search of Netflix comcast bandwidth limits will sh ow you how widespread the issue is. if netflix is something you enjoy, Id strongly recommend switching to a non comcast internet service if possible.
If you have further questions, let me know.
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Senior Technician and Network Switching Systems Operator / Maintainer.