Persistent object has been deleted

hi all

Sometime i got this exception on ivy (both engine and designer) then it's gone somehow after restarting service. Here is stacktrace:

[errorId=15D9BD0669682681, request=Ulc over HTTP POST , session=9 (ivy), application=0, requestId=7789, executionContext=SYSTEM, pmv=System$Administration$1, client=192.168.72.196]
    Caused by: ch.ivyteam.ivy.persistence.PersistentObjectDeletedException: Persistent object has been deleted [class=class ch.ivyteam.ivy.application.internal.data.ProcessModelData, id=5011]
        at ch.ivyteam.ivy.persistence.base.AbstractPersistentObjectHandle.getObject(AbstractPersistentObjectHandle.java:102)
        at ch.ivyteam.ivy.persistence.base.AbstractPersistentObjectHandle.getObject(AbstractPersistentObjectHandle.java:78)
        at ch.ivyteam.ivy.persistence.client.PersistentClientObject.getData(PersistentClientObject.java:64)
        at ch.ivyteam.ivy.persistence.client.PersistentClientObject$1.execute(PersistentClientObject.java:51)
        at ch.ivyteam.ivy.persistence.client.PersistentClientObject$1.execute(PersistentClientObject.java:1)
        at ch.ivyteam.ivy.persistence.base.AbstractPersistencyService.execute(AbstractPersistencyService.java:177)
        at ch.ivyteam.ivy.persistence.base.ClassPersistencyService.execute(ClassPersistencyService.java:673)
        at ch.ivyteam.ivy.persistence.client.PersistentClientObjectInternal.execute(PersistentClientObjectInternal.java:143)
        at ch.ivyteam.ivy.persistence.client.PersistentClientObject.execute(PersistentClientObject.java:1)
        at ch.ivyteam.ivy.persistence.client.PersistentClientObjectWithLongKey.execute(PersistentClientObjectWithLongKey.java:1)
        at ch.ivyteam.ivy.persistence.client.PersistentClientObject.getData(PersistentClientObject.java:44)
        at ch.ivyteam.ivy.application.internal.ProcessModel.getName_aroundBody0(ProcessModel.java:62)
        at ch.ivyteam.ivy.application.internal.ProcessModel.getName_aroundBody1$advice(ProcessModel.java:34)
        at ch.ivyteam.ivy.application.internal.ProcessModel.getName(ProcessModel.java:1)
        at sun.reflect.GeneratedMethodAccessor17.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at ch.ivyteam.ivy.scripting.internal.types.IvyJavaMethod.invokeImpl(IvyJavaMethod.java:73)
        ... 172 more

Does anybody has experience on it? (Env: Ivy 6.3, PosgreSQL, Linux)

Thanks