Flaky Test on PbjBlockStreamServiceIntegrationTest testFullWithSubscribersAddedDynamically

[AlfredoG87]

Description

Test testFullWithSubscribersAddedDynamically of PbjBlockStreamServiceIntegrationTest class, is failing intermittently on the CI.

-> at com.hedera.pbj.runtime.grpc.Pipelines$MapSubscriber.onNext(Pipelines.java:836)
        at app//com.hedera.block.server.pbj.PbjBlockStreamServiceIntegrationTest.verifySubscribeStreamResponse(PbjBlockStreamServiceIntegrationTest.java:767)


    2025-03-10 23:18:27.124+0000 SEVERE  [com.hedera.block.server.ack.AckHandlerImpl attemptAcks] Failed to move Block with number [2] from unverified to live storage
    java.io.FileNotFoundException: File for Block [2] not found under unverified root
    	at com.hedera.block.server.persistence.StreamPersistenceHandlerImpl.moveVerified(StreamPersistenceHandlerImpl.java:178)
    	at com.hedera.block.server.ack.AckHandlerImpl.attemptAcks(AckHandlerImpl.java:165)
    	at com.hedera.block.server.ack.AckHandlerImpl.blockVerified(AckHandlerImpl.java:115)
    	at com.hedera.block.server.verification.service.BlockVerificationServiceImpl.lambda$onBlockItemsReceived$0(BlockVerificationServiceImpl.java:73)
    	at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:718)
    	at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:510)
    	at java.base/java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:2179)
    	at com.hedera.block.server.verification.session.BlockVerificationSessionBase.finalizeVerification(BlockVerificationSessionBase.java:156)
    	at com.hedera.block.server.verification.session.BlockVerificationSessionBase.processBlockItems(BlockVerificationSessionBase.java:123)
    	at com.hedera.block.server.verification.session.BlockVerificationSessionAsync.lambda$appendBlockItems$1(BlockVerificationSessionAsync.java:74)
    	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
    	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
    	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
    	at java.base/java.lang.Thread.run(Thread.java:1583)

Steps to Reproduce

This one is hard to reproduce locally but is starting to happen rather frequently in CI checks.

Here is an example where it took 3 runs to complete:
https://github.com/hiero-ledger/hiero-block-node/actions/runs/13761381724/job/38527202661

Additional context