Issue with elasticSearch MongoDB river

I'm using rwilly's ElasticSearch MongoDB river which works on
MongoDB oplogs. I'm seeing an issue where the data I enter into
MongoDB is not available in ElasticSearch at real time.The entries
however are present in Mongo and I can see the data in the oplogs.
However, when elasticSearch is brought down and brought up again, it
then reads the entries from the oplogs and has the data it was missing
previously. Its as if writes are blocked when the elasticsearch
process is up and again, the data that I enter via mongo now cannot be
searched via elasticSearch until it is brought down and brought up
again. I'd greatly appreciate any help with this as I cant seem to
figure out why it's happening. Thanks!