Failed TimeStream insert using aws sdk on a lambda JVM - Failed when retrieving a required endpoint from AWS.

We have a Kotlin (JVM) lambda that we use to insert records into a TimeStream DB. Both are in the same region.

We are using version 2.17.100 or the aws sdk.

When busy, it often fails with a EndpointDiscoveryFailedException (based on the file name in the stack trace) exception with the message "Failed when retrieving a required endpoint from AWS." and the message in the exception cause is "unable to create new native thread". The exception is thrown by software.amazon.awssdk.core.endpointdiscovery.EndpointDiscoveryFailedException$BuilderImpl

I've searched and found some references to the exception being due to Lambda throttling, although that seems weird as there are instances of it occurring when the request rate is less than one request per second (much lower than I'd expect for lambda throttling).

Also, it consistently occurs in Endpoint Discovery while attempting to call TimeStream which to me suggests a TimeStream issue instead of Lambda throttling.

I also found reference to a timestream quota for CRUD APIS being one per second per region. That does seem to be a likely cause, the the exception message is weird AND I've seen the system handle more than one request per second.

Has anybody seen this and do they have an explanation?

Thanks