Inserting new index fails, cluster goes Red

[jmr317 (Jon)]

After attempting to insert a new index on one of my clusters, the request times out and gives me this response:
{
"statusCode": 504,
"error": "Gateway Time-out",
"message": "Client request timeout"
}

After this, I check on the health of the cluster and get this response:
{
"cluster_name": "test-cluster",
"status": "red",
"timed_out": false,
"number_of_nodes": 2,
"number_of_data_nodes": 1,
"active_primary_shards": 140,
"active_shards": 140,
"relocating_shards": 0,
"initializing_shards": 0,
"unassigned_shards": 145,
"delayed_unassigned_shards": 0,
"number_of_pending_tasks": 0,
"number_of_in_flight_fetch": 0,
"task_max_waiting_in_queue_millis": 0,
"active_shards_percent_as_number": 49.122807017543856
}

If I delete the node, status goes back to yellow:
{
"cluster_name": "test-cluster",
"status": "yellow",
"timed_out": false,
"number_of_nodes": 2,
"number_of_data_nodes": 1,
"active_primary_shards": 140,
"active_shards": 140,
"relocating_shards": 0,
"initializing_shards": 0,
"unassigned_shards": 135,
"delayed_unassigned_shards": 0,
"number_of_pending_tasks": 0,
"number_of_in_flight_fetch": 0,
"task_max_waiting_in_queue_millis": 0,
"active_shards_percent_as_number": 50.90909090909091
}

I don't have this issue when trying to insert the index on my other clusters. Does anyone have any experience with this sort of issue or know of any possibilities to remedy it?

Thanks.