Loading of Spark UI blocks for a long time when HybridStore enabled

spark.history.store.hybridStore.enabled true
spark.history.store.hybridStore.maxMemoryUsage 16g 

"qtp791499503-2688947" #2688947 daemon prio=5 os_prio=0 tid=0x00007f4044042800 nid=0x8d98 waiting for monitor entry [0x00007f3f64760000]
   java.lang.Thread.State: BLOCKED (on object monitor)
    at org.apache.spark.deploy.history.FsHistoryProvider.getAppUI(FsHistoryProvider.scala:386)
    - waiting to lock <0x00000004c64433f0> (a org.apache.spark.deploy.history.FsHistoryProvider)
    at org.apache.spark.deploy.history.HistoryServer.getAppUI(HistoryServer.scala:194)
    at org.apache.spark.deploy.history.ApplicationCache.$anonfun$loadApplicationEntry$2(ApplicationCache.scala:182)
    at org.apache.spark.deploy.history.ApplicationCache$$Lambda$805/90086258.apply(Unknown Source)
    at org.apache.spark.deploy.history.ApplicationCache.time(ApplicationCache.scala:154)
    at org.apache.spark.deploy.history.ApplicationCache.org$apache$spark$deploy$history$ApplicationCache$$loadApplicationEntry(ApplicationCache.scala:180)
    at org.apache.spark.deploy.history.ApplicationCache$$anon$1.load(ApplicationCache.scala:71)
    at org.apache.spark.deploy.history.ApplicationCache$$anon$1.load(ApplicationCache.scala:58)
    at org.sparkproject.guava.cache.LocalCache$LoadingValueReference.loadFuture(LocalCache.java:3599)
    at org.sparkproject.guava.cache.LocalCache$Segment.loadSync(LocalCache.java:2379)
    at org.sparkproject.guava.cache.LocalCache$Segment.lockedGetOrLoad(LocalCache.java:2342)
    - locked <0x000000066effc3e8> (a org.sparkproject.guava.cache.LocalCache$StrongAccessEntry)
    at org.sparkproject.guava.cache.LocalCache$Segment.get(LocalCache.java:2257)
    at org.sparkproject.guava.cache.LocalCache.get(LocalCache.java:4000)
    at org.sparkproject.guava.cache.LocalCache.getOrLoad(LocalCache.java:4004)
    at org.sparkproject.guava.cache.LocalCache$LocalLoadingCache.get(LocalCache.java:4874)
    at org.apache.spark.deploy.history.ApplicationCache.get(ApplicationCache.scala:108)
    at org.apache.spark.deploy.history.ApplicationCache.withSparkUI(ApplicationCache.scala:120)
    at org.apache.spark.deploy.history.HistoryServer.org$apache$spark$deploy$history$HistoryServer$$loadAppUi(HistoryServer.scala:251)
    at org.apache.spark.deploy.history.HistoryServer$$anon$1.doGet(HistoryServer.scala:99)

"spark-history-task-0" #49 daemon prio=5 os_prio=0 tid=0x00007f431e55b800 nid=0x1ac6 in Object.wait() [0x00007f41b2cc9000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    at java.lang.Thread.join(Thread.java:1252)
    - locked <0x000000063ccbc9f0> (a java.lang.Thread)
    at java.lang.Thread.join(Thread.java:1326)
    at org.apache.spark.deploy.history.HybridStore.close(HybridStore.scala:106)
    at org.apache.spark.status.AppStatusStore.close(AppStatusStore.scala:553)
    at org.apache.spark.deploy.history.FsHistoryProvider.$anonfun$invalidateUI$1(FsHistoryProvider.scala:913)
    at org.apache.spark.deploy.history.FsHistoryProvider.$anonfun$invalidateUI$1$adapted(FsHistoryProvider.scala:911)
    at org.apache.spark.deploy.history.FsHistoryProvider$$Lambda$416/229723341.apply(Unknown Source)
    at scala.Option.foreach(Option.scala:407)
    at org.apache.spark.deploy.history.FsHistoryProvider.invalidateUI(FsHistoryProvider.scala:911)
    - locked <0x00000004c64433f0> (a org.apache.spark.deploy.history.FsHistoryProvider)
    at org.apache.spark.deploy.history.FsHistoryProvider.$anonfun$checkForLogs$7(FsHistoryProvider.scala:541)
    at org.apache.spark.deploy.history.FsHistoryProvider.$anonfun$checkForLogs$7$adapted(FsHistoryProvider.scala:498)