Dear acalbazana ,
You may start from this KB article,
Certificate-Related Errors in Audits and Logs of t - CA Knowledge
Just a guess, when a certificate (or other entity/object) is used often, it might be cached in memory. The change on policy manage might not apply immediately due to the cache. After you restart ssg, the change will 100% take effect. Therefore, your case might be due to a change on the certificate which would cause the problem, but it didn't take effect (therefore you didn't know it) until you restarted ssg.
Restarting ssg should not change the certificate, it just reloads the certificate from database, so the change must be done before restart.
Regards,
Mark