Opensearch Serverless - Slow and fails to index

I created a simple index with the following schema (in a search collection):

PUT musers1
{
    "mappings": {
        "properties": {
            "uuid":            { "type" : "keyword" },
            "ext_id":          { "type" : "keyword" },
            "last_name":       { "type" : "text", "fields": { "raw": { "type":  "keyword" }} },
            "first_name":      { "type" : "text", "fields": { "raw": { "type":  "keyword" }} },
            "primary_location":{ "type" : "long" },
            "created_date":    { "type" : "long" },
            "permissions":     { "type" : "keyword" },
            "roles":           { "type" : "keyword" }
        }
    }
}

Then I attempted to load 73 records in the dashboard (subset of data):

POST _bulk
{"index":{"_index":"musers1","_id":"14399575-cb41-4d33-4ee2-9a69c90a18af"}}
{"created_date":1464369890,"ext_id":"1111111","first_name":"Demo","last_name":"User1","primary_location":481549029373652992,"roles":["MEMBER"],"uuid":"14399575-cb41-4d33-4ee2-9a69c90a18af"}
{"index":{"_index":"musers1","_id":"f9644fb8-e790-429a-4965-9e18be4b8d8f"}}
{"created_date":1464369890,"ext_id":"2222222","first_name":"Demo","last_name":"User2","primary_location":481549029373652992,"roles":["MEMBER"],"uuid":"f9644fb8-e790-429a-4965-9e18be4b8d8f"}
{"index":{"_index":"musers1","_id":"4a621fc9-dc93-4934-756d-450412ca2f7a"}}
{"created_date":1607376361,"ext_id":"63844","first_name":"Demo","last_name":"User3","primary_location":1183110257241493504,"roles":["MEMBER","FT-FLOOR"],"uuid":"4a621fc9-dc93-4934-756d-450412ca2f7a"}
...

And I got back the response 4 minutes later!

{
  "took": 251331,
  "errors": true,
  "items": [
...

In the end, there were 64 records indexed, and the other nine failed with the error Timeout while processing request.

Also, I loaded 2000 records (slowly and painfully) yesterday into a different index and ran a few searches against it. I ended up with 5 Search and 5 Index OCUs. These OCUs have remained since yesterday. Is it normal to have 10 OCUs active when there is no indexing or search activity?

Is it normal for 73 records to fail 12% of the time and take 4 minutes? That's 18 records per minute. If I had 20 million records to index, (I have more than that actually) it would take over 2 years to index!

I hope I am doing something wrong, because this seems too slow and too expensive...

Any ideas? Z