NVP vProxy: SQL VM restore mount fails "HTTP 409 (Conflict)"

The SQL VM restore is performed from the Data Protection Restore Client (DPRC). 
The mount process fails, reporting HTTP 409 (Conflict):

The NetWorker server's flr-server.log reports the same HTTP error:

Linx: /nsr/authc/logs/flr-server.log
Windows (Default): C:\Program Files\EMC NetWorker\nsr\authc-server\tomcat\logs\flr-server.log

YYYY-MM-DD HH:mm:SS [https-jsse-nio-9090-exec-5] INFO  c.e.n.c.v.i.VProxyRestClient.getVProxyUrl 104 - Call vProxy: POST https://NETWORKER-SERVER-ADDRESS:9090/api/v1/FlrBrowseSessions
YYYY-MM-DD HH:mm:SS [https-jsse-nio-9090-exec-5] INFO  c.e.n.c.v.i.VProxyRestClient.createVProxyHttpRequest 126 - Using already cached NW routable IP: NETWORKER-SERVER-ADDRESS/NETWORKER-SERVER-IP
YYYY-MM-DD HH:mm:SS [https-jsse-nio-9090-exec-5] INFO  c.e.n.c.v.i.VProxyRestClient._vProxyPOST 265 - Payload = {"Config":{"AcceptedLanguage":"en","acceptedLanguage":"en","SessionId":null,"LogTag":"FLR_Browse_FLR-SESSION-ID","IdleTimeout":0,"LogLevel":"DEBUG","FlrMountSessionId":"FLR-SESSION-ID","CacheRetentionSeconds":60,"CurrentWorkingDirectory":"","BrowseDestination":false,"ParentPath":null,"ApplicationData":null,"AppName":null,"Vcenter":null,"VmGuestLogin":null}}
YYYY-MM-DD HH:mm:SS [https-jsse-nio-9090-exec-5] INFO  c.e.n.c.v.i.VProxyRestClient._vProxyPOST 270 - Requesting vProxyPOST for https://NETWORKER-SERVER-ADDRESS:9090/api/v1/FlrBrowseSessions, FlrBrowseSessions...
YYYY-MM-DD HH:mm:SS [https-jsse-nio-9090-exec-5] INFO  c.e.n.c.v.i.VProxyRestClient._vProxyPOST 272 - Got vProxyPOST response.
YYYY-MM-DD HH:mm:SS [https-jsse-nio-9090-exec-5] INFO  c.e.n.c.v.i.VProxyRestClient.checkResponse 390 - Response Status Code = 409
YYYY-MM-DD HH:mm:SS [https-jsse-nio-9090-exec-5] INFO  c.e.n.c.v.i.VProxyRestClient.checkResponse 391 - Response Reason Phrase = Conflict
YYYY-MM-DD HH:mm:SS [https-jsse-nio-9090-exec-5] ERROR c.e.n.c.v.i.VProxyRestClient.checkResponse 396 - Could not connect to vproxy. Http Response status code: 409 Conflict
YYYY-MM-DD HH:mm:SS [https-jsse-nio-9090-exec-5] ERROR c.e.n.c.v.i.VProxyMount.postBrowseSession 378 - Error browsing  
com.emc.nw.common.exception.BrowseException: Could not connect to vproxy. Http Response status code: 409 Conflict
    .... Removed for brevity ....
YYYY-MM-DD HH:mm:SS [https-jsse-nio-9090-exec-5] ERROR c.e.f.s.i.FsObjectServiceImpl.createVProxyBrowse 812 - Browse backup sessions were not created correctly - possibly a bad mount for sessionid: FLR-SESSION-ID
YYYY-MM-DD HH:mm:SS [https-jsse-nio-9090-exec-5] ERROR c.e.f.s.i.FsObjectServiceImpl.createVProxyBrowse 813 - mount session error message reads: Mount job failure message: Create vProxy browse requests failed. 

The DPRC is not waiting long enough for the mount operation to complete. The DPRC sends an Application Programming Interface (API) call to close the mount session while vProxy is still mounting disks, causing an HTTP 409 conflict.

This issue was raised to NetWorker engineering.

Impacted: NetWorker 19.13.0.0 and prior

This issue is fixed in NetWorker 19.13.0.1.

Upgrade the NetWorker server to this release (or later) for a fix. 

This problem was observed in an environment where one SQL VM contained 10 disks (VMDK) and many databases. All MSVMAPPAGENT mount operations failed with this symptom, where other smaller SQL servers mounted without issue.