Found the following NPE thrown in UGI tgt renewer. The NPE was thrown within an exception handler so the original exception was hidden, though it's likely caused by expired tgt.
18/07/02 10:30:57 ERROR util.SparkUncaughtExceptionHandler: Uncaught exception in thread Thread[TGT Renewer for foo@EXAMPLE.COM,5,main]
Suspect it's related to https://bugs.openjdk.java.net/browse/JDK-8154889.
The relevant code was added in
HADOOP-13590. File this jira to handle the exception better.