This problem has happened in the past. Found link to forum post from 2017 posted by Spectrum moderator that they are working to resolve. I would contact support since it is not on your end but fault of Spectrum. Here is copied post:
Our apologies for the trouble with Spectrum TV. We are working to resolve an issue with the Spectrum TV application on all platforms.
We will have the service issue resolved as quickly as possible.
As always, we thank you for your patience while we pursue resolution!
Spectrum-Social Media Customer Care
Lead Moderator-Community Forums
In the other thread one user got it working by entering first wrong passwork and then repeating login with the correct one. He did not know why but started working after doing this. If you google this has been a frequent problem in the past after switch from TWC to Spectrum.