This article explains why the evaluation license reappears after the Junos upgrade to 21.1R1 or a later version.

This behaviour is expected if the License is not revoked and a new core-base license is not generated from the Agile portal before upgrading to Junos 21.1R1 or later.

Starting from 21.1R1, the vCPU scale license is introduced. After upgrading, vSRX automatically adds the vCPU scale license as an evaluation license for 60 days.

For more information about the vCPU core-based license and how to revoke and generate a new license key from the Agile portal, check the article below.