Can't sign in on Avast Free Antivirus dashboard

I have an account with Avast (obviously, since I wouldn’t be able to post this message otherwise.)

When I go to my dashboard and click on the sign in button on the top right, I enter my email and password, but it says the login was unsuccessful, and I get this message:

“We are sorry, but we could not connect your device to this account.”

So I try creating a new account using a new email address, but then it tells me I’m already logged in. I’m not.

I was experiencing this problem earlier, along with an inability to reactivate my AV, so I performed a full wipe and reinstall in safe mode per Avast’s instructions. The activation date has moved to 2019, which is good, but I still can’t log in.

How do I solve this?

Sign in via the my.avast.com portal.