Our system also encountered the same issue.  Here I am attaching the thread dump.

ajp-nio-0.0.0.0-8009-exec-1206 - priority:5 - threadId:0x0000000034982800 - nativeId:0x5b94 - state:BLOCKED
stackTrace:
java.lang.Thread.State: BLOCKED (on object monitor)
at ch.qos.logback.core.rolling.RollingFileAppender.subAppend(RollingFileAppender.java:169)

• waiting to lock <0x00000006c132c930> (a ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy)
  at ch.qos.logback.core.OutputStreamAppender.append(OutputStreamAppender.java:103)
  at ch.qos.logback.core.UnsynchronizedAppenderBase.doAppend(UnsynchronizedAppenderBase.java:88)
  at ch.qos.logback.core.spi.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:48)
  at ch.qos.logback.classic.Logger.appendLoopOnAppenders(Logger.java:272)
  at ch.qos.logback.classic.Logger.callAppenders(Logger.java:259)
  at ch.qos.logback.classic.Logger.buildLoggingEventAndAppend(Logger.java:441)
  at ch.qos.logback.classic.Logger.filterAndLog_0_Or3Plus(Logger.java:395)
  at ch.qos.logback.classic.Logger.warn(Logger.java:712)