I am an instructor with the free K12 account. 5 of my students and 2 of my test accounts have the same issue. This is a big problem! It will work for a while then lock the student out. I've resent invitations and sometimes that works for a while. One student could get in on her phone but not PC (although it was signed in on both before) - another could get in on her phone from emails with a link for feedback - then go back to dashboard - but only on her phone not on desktop (it's really hard to type etc on the phone - this is not sustainable)
This makes Canvas look like an unstable platform! I chose it because it was so widely used ... I'm getting parent emails almost daily!
I've posted on the community before - I've made a ticket - I've sent an email to a tech help .. no answers 😞 Disappointed