When a user accesses the Self Service portal with a Registered Computer 1.12 credential, the user is prompted to authenticate using the next available credential type (not with the existing Registered Computer credential).
Additionally, if the account policy is set to enable auto-upgrade, the Self Service Portal will not automatically upgrade the credential to version 1.16.
There is no workaround for this issue.
After authenticating to the Self Service Portal, the user must click Register your Computer to upgrade the credential to the 1.16 version.