The same issue with 14.2 servers and 14.0.0 clients, The issue is not reproduced with 14.0.0 server and 12.3 client

Reproduction:
1. generate my-stateful-with-db bluprint (add this to space properties) properties.setProperty("cluster-config.groups.group.repl-policy.redo-log-memory-capacity","0");
strat the demo
2. undeploy mirror
3. run a client from 12.3 that writes and change objects
4. redeploy the mirror
see exceptions in space log:
2020-12-08 16:45:38,106 my-app-space.1 [1] SEVERE [com.gigaspaces.replication.backlog.primary-backup-reliable-async-mirror-1] - Redo log file integrity validation failed; Caused by: com.gigaspaces.internal.server.space.redolog.storage.bytebuffer.ByteBufferStorageCompromisedException: Error while checking data integrity, reached packet index 100
at com.gigaspaces.internal.server.space.redolog.storage.bytebuffer.ByteBufferRedoLogFileStorage.validateIntegrity(ByteBufferRedoLogFileStorage.java:781)
at com.gigaspaces.internal.server.space.redolog.storage.BufferedRedoLogFileStorageDecorator.validateIntegrity(BufferedRedoLogFileStorageDecorator.java:173)
at com.gigaspaces.internal.server.space.redolog.storage.CacheLastRedoLogFileStorageDecorator.validateIntegrity(CacheLastRedoLogFileStorageDecorator.java:130)
at com.gigaspaces.internal.server.space.redolog.FixedSizeSwapRedoLogFile.validateIntegrity(FixedSizeSwapRedoLogFile.java:271)
at com.gigaspaces.internal.cluster.node.impl.backlog.AbstractSingleFileGroupBacklog.validateIntegrity(AbstractSingleFileGroupBacklog.java:1304)
at com.gigaspaces.internal.cluster.node.impl.backlog.AbstractSingleFileGroupBacklog.getPacketsUnsafe(AbstractSingleFileGroupBacklog.java:943)
at com.gigaspaces.internal.cluster.node.impl.backlog.multisourcesinglefile.MultiSourceSingleFileReliableAsyncGroupBacklog.getReliableAsyncPackets(MultiSourceSingleFileReliableAsyncGroupBacklog.java:265)
at com.gigaspaces.internal.cluster.node.impl.groups.reliableasync.ReliableAsyncReplicationSourceChannel.getPendingPackets(ReliableAsyncReplicationSourceChannel.java:97)
at com.gigaspaces.internal.cluster.node.impl.groups.async.AsyncReplicationSourceChannel$AsyncDispatcher.call(AsyncReplicationSourceChannel.java:250)
at com.gigaspaces.internal.cluster.node.impl.groups.async.AsyncReplicationSourceChannel$AsyncDispatcher.call(AsyncReplicationSourceChannel.java:211)
at com.gigaspaces.internal.utils.concurrent.ScheduledThreadPoolAsyncHandlerProvider$AsyncRunnableWrapper$ExecutionTask.run(ScheduledThreadPoolAsyncHandlerProvider.java:297)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
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)
Caused by: java.lang.ClassNotFoundException: Unknown class code: 3
at com.gigaspaces.internal.io.IOUtils.readObject(IOUtils.java:736)
at com.gigaspaces.internal.client.mutators.SetValueSpaceEntryMutator.readExternal(SetValueSpaceEntryMutator.java:63)
at java.io.ObjectInputStream.readExternalData(ObjectInputStream.java:2118)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2067)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:431)
at java.util.LinkedList.readObject(LinkedList.java:1149)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1170)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2178)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2069)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:431)
at com.gigaspaces.internal.serialization.ObjectClassSerializer.read(ObjectClassSerializer.java:37)
at com.gigaspaces.internal.io.IOUtils.readObject(IOUtils.java:738)
at com.gigaspaces.internal.cluster.node.impl.packets.data.operations.ChangeReplicationPacketData.readExternalImpl(ChangeReplicationPacketData.java:346)
at com.gigaspaces.internal.cluster.node.impl.packets.data.operations.ChangeReplicationPacketData.readFromSwap(ChangeReplicationPacketData.java:383)
at com.gigaspaces.internal.io.IOUtils.readSwapExternalizableObject(IOUtils.java:895)
at com.gigaspaces.internal.cluster.node.impl.backlog.globalorder.GlobalOrderOperationPacket.readFromSwap(GlobalOrderOperationPacket.java:106)
at com.gigaspaces.internal.io.IOUtils.readSwapExternalizableObject(IOUtils.java:895)
at com.gigaspaces.internal.server.space.redolog.storage.bytebuffer.SwapPacketStreamSerializer.readPacketFromStream(SwapPacketStreamSerializer.java:43)
at com.gigaspaces.internal.cluster.node.impl.backlog.AbstractSingleFileGroupBacklog$1.readPacketFromStream(AbstractSingleFileGroupBacklog.java:383)
at com.gigaspaces.internal.cluster.node.impl.backlog.AbstractSingleFileGroupBacklog$1.readPacketFromStream(AbstractSingleFileGroupBacklog.java:373)
at com.gigaspaces.internal.server.space.redolog.storage.bytebuffer.PacketSerializer$InputStreamsResource.readPacket(PacketSerializer.java:132)
at com.gigaspaces.internal.server.space.redolog.storage.bytebuffer.PacketSerializer.deserializePacket(PacketSerializer.java:100)
at com.gigaspaces.internal.server.space.redolog.storage.bytebuffer.ByteBufferRedoLogFileStorage.validateIntegrity(ByteBufferRedoLogFileStorage.java:756)
... 17 more