Artifact Signing organization identity validation link returns "You need permission" (signs in to wrong tenant) for an authorized user

Our Public organization identity validation for Artifact Signing is in Action Required. Both the verification email link and the portal's "Please complete your verification here" link open credentials.microsoft.com/verify/noPermission with:

"You need permission. You are currently logged in as [my work email] on Entra Azure tenant [our Microsoft 365 tenant]. To access this page, you must be logged in as an authorized user of the Entra Azure tenant which was used for the enrollment application or change."

The page signs the primary-email user into that account's home tenant (our Microsoft 365 tenant), not the tenant that holds the subscription and the signing account. The primary-email user is a guest in the enrollment tenant and holds the Artifact Signing Identity Verifier role on the signing account. The request was created by the subscription Owner, who also holds Identity Verifier on the account.

Tried so far: InPrivate window, signed in to portal.azure.com in the enrollment tenant first, opened the portal continuation link from there. Also tried the Owner account. Same result each time. The request has not been recreated or duplicated.