This is de debug.log on the first time it happend:
2018-09-09 23:57:01.599+0000 ERROR [o.n.b.v.r.ErrorReporter] Client triggered an unexpected error [Neo.DatabaseError.General.UnknownError]: Relationship[74825438,used=false,source=-1,target=-1,type=-1,sCount=1,sNext=-1,tCount=1,tNext=-1,prop=-1,secondaryUnitId=-1, sFirst, tFirst] not in use, reference 6f0094cf-7869-4625-bd68-8baf60f574aa.
2018-09-09 23:57:01.599+0000 ERROR [o.n.b.v.r.ErrorReporter] Client triggered an unexpected error [Neo.DatabaseError.General.UnknownError]: Relationship[74825438,used=false,source=-1,target=-1,type=-1,sCount=1,sNext=-1,tCount=1,tNext=-1,prop=-1,secondaryUnitId=-1, sFirst, tFirst] not in use, reference 6f0094cf-7869-4625-bd68-8baf60f574aa. Relationship[74825438,used=false,source=-1,target=-1,type=-1,sCount=1,sNext=-1,tCount=1,tNext=-1,prop=-1,secondaryUnitId=-1, sFirst, tFirst] not in use
org.neo4j.kernel.impl.store.InvalidRecordException: Relationship[74825438,used=false,source=-1,target=-1,type=-1,sCount=1,sNext=-1,tCount=1,tNext=-1,prop=-1,secondaryUnitId=-1, sFirst, tFirst] not in use
at org.neo4j.kernel.impl.store.record.RecordLoad.verify(RecordLoad.java:63)
at org.neo4j.kernel.impl.store.CommonAbstractStore.verifyAfterReading(CommonAbstractStore.java:1188)
at org.neo4j.kernel.impl.store.CommonAbstractStore.readIntoRecord(CommonAbstractStore.java:1062)
at org.neo4j.kernel.impl.store.CommonAbstractStore.getRecord(CommonAbstractStore.java:1021)
at org.neo4j.kernel.impl.transaction.state.Loaders$3.load(Loaders.java:219)
at org.neo4j.kernel.impl.transaction.state.Loaders$3.load(Loaders.java:209)
at org.neo4j.kernel.impl.transaction.state.RecordChanges.getOrLoad(RecordChanges.java:68)
at org.neo4j.kernel.impl.transaction.state.RelationshipDeleter.disconnect(RelationshipDeleter.java:81)
at org.neo4j.kernel.impl.transaction.state.RelationshipDeleter.disconnectRelationship(RelationshipDeleter.java:68)
at org.neo4j.kernel.impl.transaction.state.RelationshipDeleter.relDelete(RelationshipDeleter.java:58)
at org.neo4j.kernel.impl.transaction.state.TransactionRecordState.relDelete(TransactionRecordState.java:281)
at org.neo4j.kernel.impl.storageengine.impl.recordstorage.TransactionToRecordStateVisitor.visitDeletedRelationship(TransactionToRecordStateVisitor.java:102)
at org.neo4j.storageengine.api.txstate.TxStateVisitor$Delegator.visitDeletedRelationship(TxStateVisitor.java:195)
at org.neo4j.storageengine.api.txstate.TxStateVisitor$Delegator.visitDeletedRelationship(TxStateVisitor.java:195)
at org.neo4j.kernel.api.txstate.TransactionCountingStateVisitor.visitDeletedRelationship(TransactionCountingStateVisitor.java:106)
at org.neo4j.kernel.impl.api.state.TxState$8.visitRemoved(TxState.java:287)
at org.neo4j.kernel.impl.api.state.TxState$8.visitRemoved(TxState.java:283)
at org.neo4j.kernel.impl.util.diffsets.SuperDiffSets.accept(SuperDiffSets.java:70)
at org.neo4j.kernel.impl.util.diffsets.RelationshipDiffSets.accept(RelationshipDiffSets.java:39)
at org.neo4j.kernel.impl.api.state.TxState.accept(TxState.java:206)
at org.neo4j.kernel.impl.storageengine.impl.recordstorage.RecordStorageEngine.createCommands(RecordStorageEngine.java:307)
at org.neo4j.kernel.impl.api.KernelTransactionImplementation.commit(KernelTransactionImplementation.java:643)
at org.neo4j.kernel.impl.api.KernelTransactionImplementation.closeTransaction(KernelTransactionImplementation.java:550)
at org.neo4j.internal.kernel.api.Transaction.close(Transaction.java:189)
at org.neo4j.bolt.v1.runtime.TransactionStateMachine$State.closeTransaction(TransactionStateMachine.java:407)
at org.neo4j.bolt.v1.runtime.TransactionStateMachine$State$1.streamResult(TransactionStateMachine.java:292)
at org.neo4j.bolt.v1.runtime.TransactionStateMachine.streamResult(TransactionStateMachine.java:104)
at org.neo4j.bolt.v1.runtime.BoltStateMachine$State$3.pullAll(BoltStateMachine.java:508)
at org.neo4j.bolt.v1.runtime.BoltStateMachine.pullAll(BoltStateMachine.java:267)
at org.neo4j.bolt.v1.messaging.BoltMessageRouter.lambda$onPullAll$6(BoltMessageRouter.java:114)
at org.neo4j.bolt.runtime.MetricsReportingBoltConnection.lambda$enqueue$0(MetricsReportingBoltConnection.java:69)
at org.neo4j.bolt.runtime.DefaultBoltConnection.processNextBatch(DefaultBoltConnection.java:195)
at org.neo4j.bolt.runtime.MetricsReportingBoltConnection.processNextBatch(MetricsReportingBoltConnection.java:87)
at org.neo4j.bolt.runtime.DefaultBoltConnection.processNextBatch(DefaultBoltConnection.java:143)
at org.neo4j.bolt.runtime.ExecutorBoltScheduler.executeBatch(ExecutorBoltScheduler.java:170)
at org.neo4j.bolt.runtime.ExecutorBoltScheduler.lambda$scheduleBatchOrHandleError$2(ExecutorBoltScheduler.java:153)
at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1590)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)