I am getting concurrent modification error using a connector, what can be the cause?

Hi,

I needed to call a connector many times in a row, i created a call activity with iteration (sequential multi-instantiation). After a while it stops working with ConcurrentModificationException, after starting it over again it doesnt stop with the same data, it stops randomly. I started over again and again, always deleting the elements that was already finished, after 7 restarts it finished.

To me it looked like a random error, what causes this error? How to get around this?

It is really frustrating since i am creating invoices with this process, and stops working randomly doesnt do any good, since i cant just say lets restart, i need to check how far it got in the object list, and i need to remove those elements that was finished. Today i did this with ~470 objects and ~7 restarts.

This is the error:

2021-01-28 07:00:37.372 +0000 SEVERE: org.bonitasoft.engine.execution.work.InSessionBonitaWork THREAD_ID=78 | HOSTNAME=666f17a32b35 | TENANT_ID=1 | The work [ExecuteConnectorOfActivity: flowNodeInstanceId = 9041417, connectorDefinitionName = szamlazzhuKifizetes] failed. The failure will be handled.
2021-01-28 07:00:37.378 +0000 FINE: org.bonitasoft.engine.core.process.instance.impl.ActivityInstanceServiceImpl THREAD_ID=78 | HOSTNAME=666f17a32b35 | TENANT_ID=1 | [SAutomaticTaskInstance with id 9,041,417] changed state 37->3(new=FailedActivityStateImpl)
2021-01-28 07:00:37.392 +0000 FINE: org.bonitasoft.engine.core.process.instance.event.impl.EventInstanceServiceImpl THREAD_ID=78 | HOSTNAME=666f17a32b35 | TENANT_ID=1 | Created end event with id = <9041418>, parent process instance id = <66185>, root process instance id = <66129>, process definition id = <5435921866928010583>
2021-01-28 07:00:37.404 +0000 WARNING: org.bonitasoft.engine.execution.event.ErrorEventHandlerStrategy THREAD_ID=78 | HOSTNAME=666f17a32b35 | TENANT_ID=1 | No catch error event was defined to handle the error code 'szamlazzhuError' defined in the process [name: SzamlaJovairas, version: 1.0], throw event: szamlazzhuError. This throw error event will act as a Terminate Event.
2021-01-28 07:00:37.406 +0000 FINE: org.bonitasoft.engine.persistence.TenantHibernatePersistenceService THREAD_ID=78 | HOSTNAME=666f17a32b35 | [Tenant] Deleting instance of class SEndEventInstance with id=9041418
2021-01-28 07:00:37.411 +0000 SEVERE: org.bonitasoft.engine.execution.work.InSessionBonitaWork THREAD_ID=78 | HOSTNAME=666f17a32b35 | TENANT_ID=1 | java.util.ConcurrentModificationException : "No message"
java.util.ConcurrentModificationException
at java.base/java.util.HashMap$HashIterator.nextNode(HashMap.java:1493)
at java.base/java.util.HashMap$KeyIterator.next(HashMap.java:1516)
at org.bonitasoft.engine.core.connector.impl.ConnectorServiceImpl.buildConnectorInputMessage(ConnectorServiceImpl.java:147)
at org.bonitasoft.engine.core.connector.impl.ConnectorServiceImpl.executeConnector(ConnectorServiceImpl.java:163)
at org.bonitasoft.engine.connector.ConnectorServiceDecorator.executeConnector(ConnectorServiceDecorator.java:115)
at org.bonitasoft.engine.execution.work.ExecuteConnectorWork.work(ExecuteConnectorWork.java:153)
at org.bonitasoft.engine.execution.work.failurewrapping.TxInHandleFailureWrappingWork.work(TxInHandleFailureWrappingWork.java:41)
at org.bonitasoft.engine.execution.work.failurewrapping.TxInHandleFailureWrappingWork.work(TxInHandleFailureWrappingWork.java:41)
at org.bonitasoft.engine.execution.work.failurewrapping.TxInHandleFailureWrappingWork.work(TxInHandleFailureWrappingWork.java:41)
at org.bonitasoft.engine.execution.work.failurewrapping.TxInHandleFailureWrappingWork.work(TxInHandleFailureWrappingWork.java:41)
at org.bonitasoft.engine.execution.work.InSessionBonitaWork.work(InSessionBonitaWork.java:59)
at org.bonitasoft.engine.work.BonitaThreadPoolExecutor.lambda$submit$1(BonitaThreadPoolExecutor.java:103)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)

2021-01-28 07:00:37.507 +0000 SEVERE: org.bonitasoft HTTP/1.1 200 200---------200------
2021-01-28 07:00:37.507 +0000 SEVERE: org.bonitasoft Date : Thu, 28 Jan 2021 07:00:37 GMT
2021-01-28 07:00:37.507 +0000 SEVERE: org.bonitasoft Server : Apache/2.4.38 (Debian)
2021-01-28 07:00:37.507 +0000 SEVERE: org.bonitasoft Set-Cookie : JSESSIONID=ACF61EFFEA6E6EA095AA63F9F2E3309C.sas3; Path=/szamla; Secure; HttpOnly
2021-01-28 07:00:37.507 +0000 SEVERE: org.bonitasoft Cache-Control : no-store, no-cache, must-revalidate, post-check=0, pre-check=0, max-age=0
2021-01-28 07:00:37.507 +0000 SEVERE: org.bonitasoft Pragma : public
2021-01-28 07:00:37.507 +0000 SEVERE: org.bonitasoft Set-Cookie : cookie_is_member=true; Max-Age=31536000; Expires=Fri, 28-Jan-2022 07:00:37 GMT; Path=/; Secure
2021-01-28 07:00:37.507 +0000 SEVERE: org.bonitasoft Content-Disposition : attachment; filename=a58gg9frdxa9kj64pfw55553.xml
2021-01-28 07:00:37.507 +0000 SEVERE: org.bonitasoft Content-Type : application/octet-stream
2021-01-28 07:00:37.507 +0000 SEVERE: org.bonitasoft Content-Length : 311
2021-01-28 07:00:37.507 +0000 SEVERE: org.bonitasoft Expires : Thu, 28 Jan 2021 07:00:37 GMT
2021-01-28 07:00:37.507 +0000 SEVERE: org.bonitasoft Keep-Alive : timeout=15, max=1000
2021-01-28 07:00:37.507 +0000 SEVERE: org.bonitasoft Connection : Keep-Alive
2021-01-28 07:00:37.508 +0000 FINE: org.bonitasoft.engine.connector.impl.ConnectorExecutorImpl THREAD_ID=88 | HOSTNAME=666f17a32b35 | TENANT_ID=1 | Finish execution of connector class org.bonitasoft.engine.core.connector.impl.SConnectorAdapter