hibernate second level cache keeps emptying itself - spring

Question

Have a Spring/Tomcat application and I'm trying to get ehcache working as Hibernate second-level entity cache. It is enabled and active. I can see in the debug log output how many entities are cached. The problem is that every few seconds, the cache empties. I even pinned the cache (just to see if that would alter the behavior) and now I see this:
05-08-2017 16:05:21.550 [taskExecutor-12] {env=''} WARN n.s.e.Cache: Data availability impacted:
****************************************************************************************
************************** removeAll called on a pinned cache **************************
05-08-2017 16:05:21.550 [taskExecutor-12] {env=''} WARN n.s.e.Cache: Data availability impacted:
****************************************************************************************
************************** removeAll called on a pinned cache **************************
So I think this is the problem. Any idea what would cause removeAll to be implicitly called over and over?
ehcache.xml
<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="ehcache.xsd"
updateCheck="true"
monitoring="autodetect"
maxBytesLocalHeap="24G"
dynamicConfig="true">
<defaultCache eternal="true" maxBytesLocalHeap="1" /> <!-- not used, but required per ehcache configuration rules -->
<!-- cache for foo -->
<cache name="foo"
maxBytesLocalHeap="8G"
eternal="false"
memoryStoreEvictionPolicy="LRU"
timeToLiveSeconds="12000"
transactionalMode="off">
<pinning store="inCache" />
<persistence strategy="none" />
</cache>
</ehcache>
persistence.xml
<properties>
<property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect" />
<property name="hibernate.connection.driver_class" value="org.postgresql.Driver" />
<property name="hibernate.show_sql" value="false" />
<property name="hibernate.hbm2ddl.auto" value="update" />
<property name="hibernate.ejb.naming_strategy" value="org.hibernate.cfg.ImprovedNamingStrategy" />
<property name="hibernate.cache.provider_class" value="org.hibernate.cache.EhCacheProvider" />
<property name="hibernate.cache.use_second_level_cache" value="true" />
<property name="hibernate.cache.use_query_cache" value="false" />
<property name="hibernate.generate_statistics" value="true" />
<property name="hibernate.cache.use_structured_entries" value="true" />
<property name="hibernate.cache.region.factory_class" value="org.hibernate.cache.ehcache.SingletonEhCacheRegionFactory" />
</properties>
And these annotations are on the entity model class:
#Cacheable
#Cache(region = "foo", usage = CacheConcurrencyStrategy.READ_WRITE)

Answer 1

I figure it out. Native SQL DELETE queries were causing hibernate to frequently dump the entire cache (the removeAll calls above). I did as suggested below, and everything is working now.
2nd level cache invalidation with native queries