Update upgrade-specific.mdx

website/content/docs/upgrading/upgrade-specific.mdx

@@ -19,6 +19,7 @@ upgrade flow.
 #### Service mesh compatibility ((#service-mesh-compatibility-1-15))
 
 Upgrade to **Consul version 1.15.2 or later**.
+If using [Vault Enterprise as CA](#vault-enterprise-as-ca-1-15), **avoid Consul version 1.15.6**.
 
 Consul versions 1.15.0 - 1.15.1 contain a race condition that can cause
 some service instances to lose their ability to communicate in the mesh after
@@ -27,6 +28,15 @@ due to a problem with leaf certificate rotation.
 
 This bug is fixed in Consul versions 1.15.2 and newer.
 
+#### Vault Enterprise as CA ((#vault-enterprise-as-ca-1-15))
+Using Vault as CA with Consul version 1.15.6 will fail to initialize the CA if [`namespace`](/consul/docs/connect/ca/vault#namespace) is set
+but [`intermediate_pki_namespace`](/consul/docs/connect/ca/vault#intermediatepkinamespace) or [`root_pki_namespace`](/consul/docs/connect/ca/vault#rootpkinamespace)
+are empty. This is a bug which will be fixed in a future version.
+
+To work around this issue, users must explicitly set [`intermediate_pki_namespace`](/consul/docs/connect/ca/vault#intermediatepkinamespace) and
+[`root_pki_namespace`](/consul/docs/connect/ca/vault#rootpkinamespace) to the same value as [`namespace`](/consul/docs/connect/ca/vault#namespace).
+Set your configuration by calling [set-config](/consul/commands/connect/ca#set-config) then use [get-config](/consul/commands/connect/ca#get-config) to check.
+
 #### Removing configuration options
 
 The `connect.enable_serverless_plugin` configuration option was removed. Lambda integration is now enabled by default.