ConcurrentModificationException in notifyChangedReadersObservers

org.apache.hadoop.hbase.DroppedSnapshotException: region: .META.,,1
        at org.apache.hadoop.hbase.regionserver.HRegion.internalFlushcache(HRegion.java:876)
        at org.apache.hadoop.hbase.regionserver.HRegion.flushcache(HRegion.java:772)
        at org.apache.hadoop.hbase.regionserver.MemcacheFlusher.flushRegion(MemcacheFlusher.java:220)
        at org.apache.hadoop.hbase.regionserver.MemcacheFlusher.run(MemcacheFlusher.java:130)
Caused by: java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
        at java.util.HashMap$KeyIterator.next(HashMap.java:828)
        at org.apache.hadoop.hbase.regionserver.HStore.notifyChangedReadersObservers(HStore.java:734)
        at org.apache.hadoop.hbase.regionserver.HStore.updateReaders(HStore.java:722)
        at org.apache.hadoop.hbase.regionserver.HStore.internalFlushCache(HStore.java:691)
        at org.apache.hadoop.hbase.regionserver.HStore.flushCache(HStore.java:627)
        at org.apache.hadoop.hbase.regionserver.HRegion.internalFlushcache(HRegion.java:863)
        ... 3 more