I have resolved this. My startup directory in the Azure portal was set to Last Accessed. My last access happened to be a demo subscription that expired, which is what was triggering the sign-in error.
To get in, I signed into a different directory directly by using a URL like this: https://portal.azure.com/<tenant-ID>. Once I got successfully signed in I changed my Startup Directory to my permanent company tenant so this issue does not come up again.
It would have been helpful if the error message was more descriptive and able to tell me that I was trying to sign in to a directory that was expired and even better, if it would ask me to choose a different directory instead.