I just switched to Spectrum and Discovery Channel is not showing up in Channels. All of the other Discovery-owned channels are showing up though. I went to Discovery's website and confirmed that I can watch it via TVE, but it will not show up in Channels.
I also have Spectrum TVE. I never watch Discovery on Channels but I checked mine when I saw your post and it was missing in the lineup while other Discovery channels were present. I went to sources and re-scanned Spectrum channels. In the list Discovery [6101] was present but grayed out with an error that said something like package not authorized. So I did the individual scan just for Discovery {chan 6101] and it then added it to my channels and it is now active and working for me -- no guide data though.