This KB provides detailed information regarding the "error: certificate 'mist-device-cert': check validity period.", offering additional insights.

• Users encounter the following error consistently whenever attempting to commit any configuration changes.

mist@SRX-JTAC# commit

node0:

configuration check succeeds

node1:

error: certificate 'mist-device-cert': check validity period .

error: configuration check-out failed

node0:

error: remote commit-configuration failed on node1

error: commit failed

{primary:node0}[edit]

• The command output of >show security pki local-certificate reveals that the certificate is expired, which aligns with the observed error.
• The WAN Edge Events shows the following error:
  • 

On the CLI of the SRX delete the Client-Cert reference (meaning delete the reference to "mist-device-cert" in the config) that can be found in the Outbound-SSH hierarchy.

After that it will let you (and Mist) commit.

Modern Mist makes no use of such client certificate.