After a few days of reguluar operation, the recently changed pages on the frontpage won't update. The Index Queue under Content Indexing shows that the last processed date is a long time in the past. After investigating the logfile catalina.out, the following exception seems to be the problem:

Exception in thread "Indexer: 1" org.springframework.transaction.UnexpectedRollbackException: Transaction rolled back because it has been marked as rollback-only
at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:626)
at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:139)
at com.atlassian.confluence.search.lucene.DefaultObjectQueueWorker.run(DefaultObjectQueueWorker.java:51)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)

This exception is duplicated for multiple (all?) indexers.

After investigating the issue further, I found that a stale lockfile was in the Confluence working directory under index, called write.lock. After removing this file and restarting Confluence everything is working again.