RavenDB BulkInsert Could not flush in the specified timeout

Question

I use BulkInsert to update ~600k items in RavenDB 3.5. I use Parallel.ForEach, but after a few minutes I get this error:

System.TimeoutException: Could not flush in the specified timeout, server probably not responding or responding too slowly.
Are you writing very big documents?
   at Raven.Client.Document.RemoteBulkInsertOperation.Write(String id, RavenJObject metadata, RavenJObject data, Nullable`1 dataSize)
   at Raven.Client.Document.BulkInsertOperation.Store(Object entity, String id)

I use this BulkInsertOptions:

BatchSize = 128,
WriteTimeoutMilliseconds = 60000,
OverwriteExisting = true,
ChunkedBulkInsertOptions = null