I am doing migration of data about 330 million records and about after completion if 85% I got below exception from sink connector. 

{
"name": "mongo-sink-assets-shard24",
"connector":

{ "state": "RUNNING", "worker_id": "xxx.xxx.xxx.xxx:9083" }

,
"tasks": [

{ "id": 0, "state": "FAILED", "worker_id": "xxx.xxx.xxx.xxx:9083", "trace": "org.apache.kafka.connect.errors.ConnectException: Exiting WorkerSinkTask due to unrecoverable exception.\n\tat org.apache.kafka.connect.runtime.WorkerSinkTask.deliverMessages(WorkerSinkTask.java:561)\n\tat org.apache.kafka.connect.runtime.WorkerSinkTask.poll(WorkerSinkTask.java:322)\n\tat org.apache.kafka.connect.runtime.WorkerSinkTask.iteration(WorkerSinkTask.java:224)\n\tat org.apache.kafka.connect.runtime.WorkerSinkTask.execute(WorkerSinkTask.java:192)\n\tat org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:177)\n\tat org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:227)\n\tat java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)\n\tat java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)\n\tat java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)\n\tat java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)\n\tat java.base/java.lang.Thread.run(Thread.java:830)\nCaused by: java.lang.NullPointerException\n\tat com.mongodb.kafka.connect.sink.MongoSinkTask.processSinkRecords(MongoSinkTask.java:184)\n\tat com.mongodb.kafka.connect.sink.MongoSinkTask.lambda$put$2(MongoSinkTask.java:117)\n\tat java.base/java.util.ArrayList.forEach(ArrayList.java:1507)\n\tat com.mongodb.kafka.connect.sink.MongoSinkTask.lambda$put$3(MongoSinkTask.java:116)\n\tat java.base/java.util.HashMap.forEach(HashMap.java:1338)\n\tat com.mongodb.kafka.connect.sink.MongoSinkTask.put(MongoSinkTask.java:114)\n\tat org.apache.kafka.connect.runtime.WorkerSinkTask.deliverMessages(WorkerSinkTask.java:539)\n\t... 10 more\n" }

],
"type": "sink"
}

Error from connect.log

[2020-04-19 17:09:41,322] ERROR Mongodb bulk write (partially) failed (com.mongodb.kafka.connect.sink.MongoSinkTask:181)
com.mongodb.MongoBulkWriteException: Bulk write operation error on server 10.74.1.50:27021. Write errors: [BulkWriteError{index=305, code=28, message='Cannot create field 'sha256' in element

{xmpCameraRaw: "<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 5.6-c140 79.160451, 2017/05/06-01:08:21 "> <rdf:RDF xmlns:rdf="http://www.w3.org/1..."}

', details={}}].
at com.mongodb.connection.BulkWriteBatchCombiner.getError(BulkWriteBatchCombiner.java:173)
at com.mongodb.connection.BulkWriteBatchCombiner.throwOnError(BulkWriteBatchCombiner.java:202)
at com.mongodb.connection.BulkWriteBatchCombiner.getResult(BulkWriteBatchCombiner.java:143)
at com.mongodb.operation.BulkWriteBatch.getResult(BulkWriteBatch.java:227)
at com.mongodb.operation.MixedBulkWriteOperation.executeBulkWriteBatch(MixedBulkWriteOperation.java:282)
at com.mongodb.operation.MixedBulkWriteOperation.access$700(MixedBulkWriteOperation.java:72)
at com.mongodb.operation.MixedBulkWriteOperation$1.call(MixedBulkWriteOperation.java:205)
at com.mongodb.operation.MixedBulkWriteOperation$1.call(MixedBulkWriteOperation.java:196)
at com.mongodb.operation.OperationHelper.withReleasableConnection(OperationHelper.java:501)
at com.mongodb.operation.MixedBulkWriteOperation.execute(MixedBulkWriteOperation.java:196)
at com.mongodb.operation.MixedBulkWriteOperation.execute(MixedBulkWriteOperation.java:71)
at com.mongodb.client.internal.MongoClientDelegate$DelegateOperationExecutor.execute(MongoClientDelegate.java:213)
at com.mongodb.client.internal.MongoCollectionImpl.executeBulkWrite(MongoCollectionImpl.java:476)
at com.mongodb.client.internal.MongoCollectionImpl.bulkWrite(MongoCollectionImpl.java:456)
at com.mongodb.kafka.connect.sink.MongoSinkTask.processSinkRecords(MongoSinkTask.java:177)
at com.mongodb.kafka.connect.sink.MongoSinkTask.lambda$put$2(MongoSinkTask.java:117)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1507)
at com.mongodb.kafka.connect.sink.MongoSinkTask.lambda$put$3(MongoSinkTask.java:116)
at java.base/java.util.HashMap.forEach(HashMap.java:1338)
at com.mongodb.kafka.connect.sink.MongoSinkTask.put(MongoSinkTask.java:114)
at org.apache.kafka.connect.runtime.WorkerSinkTask.deliverMessages(WorkerSinkTask.java:539)
at org.apache.kafka.connect.runtime.WorkerSinkTask.poll(WorkerSinkTask.java:322)
at org.apache.kafka.connect.runtime.WorkerSinkTask.iteration(WorkerSinkTask.java:224)
at org.apache.kafka.connect.runtime.WorkerSinkTask.execute(WorkerSinkTask.java:192)
at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:177)
at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:227)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:830)

I am using "writemodel.strategy" default value. 

Can you please suggest what could cause this? 

Thanks,

Rajaramesh.