ClassCastException on ReadParams.getSingleQualifier

Hi all,

Recently on our prod environment we faced the following error:

 java.lang.ClassCastException: java.util.HashMap$Node cannot be cast to java.lang.String
     at 
 `de.hybris.platform.servicelayer.internal.converter.ReadParams.getSingleQualifier(ReadParams.java:103) ~[coreserver.jar:?]
     at de.hybris.platform.servicelayer.internal.model.impl.JaloPersistenceObject.readRawValue(JaloPersistenceObject.java:109) ~[coreserver.jar:?]
     at de.hybris.platform.servicelayer.internal.converter.impl.ItemModelConverter.readSingleAttribute(ItemModelConverter.java:1371) ~[coreserver.jar:?]
     at de.hybris.platform.servicelayer.internal.converter.impl.ItemAttributeProvider.getAttribute(ItemAttributeProvider.java:108) ~[coreserver.jar:?]
     at de.hybris.platform.servicelayer.model.ItemModelContextImpl.loadUnlocalizedAttribute(ItemModelContextImpl.java:285) ~[coreserver.jar:?]
     at 

There were a lot of these errors (about 1047 ones) and on different rest services we have and at some time period - within about 3 hours until we restart the node. Restart of hybris on that node resolved it - but we need to understand how is it possible?

Also the strange thing is - it give us a stack trace only for the first three times and than trows just:

 Unexpected server error:
 java.lang.ClassCastException: null

Any idea?

Thank you.