When Confluence gets stuck, the only way to get it back working is to restart the Linux service.
Logs show nothing except stuck threads such as:
09-Oct-2018 14:50:30.903 WARNING [ContainerBackgroundProcessor[StandardEngine[Standalone]]] org.apache.catalina.valves.StuckThreadDetectionValve.notifyStuckThreadDetected Thread [http-nio-8090-exec-48] (id=[8284]) has been active for [71,488] milliseconds (since [10/9/18 2:49 PM]) to serve the same request for [http://localhost:8090/] and may be stuck (configured threshold for this StuckThreadDetectionValve is [60] seconds). There is/are [31] thread(s) in total that are monitored by this Valve and may be stuck.
java.lang.Throwable
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.onSuppressedException(DefaultSingletonBeanRegistry.java:269)
at org.springframework.beans.factory.support.AbstractBeanFactory.getTypeForFactoryBean(AbstractBeanFactory.java:1488)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.getTypeForFactoryBean(AbstractAutowireCapableBeanFactory.java:808)
at org.springframework.beans.factory.support.AbstractBeanFactory.isTypeMatch(AbstractBeanFactory.java:544)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doGetBeanNamesForType(DefaultListableBeanFactory.java:447)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanNamesForType(DefaultListableBeanFactory.java:423)
at org.springframework.beans.factory.BeanFactoryUtils.beanNamesForTypeIncludingAncestors(BeanFactoryUtils.java:220)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1177)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1116)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1014)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1292)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1199)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:543)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:342)
at sun.reflect.GeneratedMethodAccessor183.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.atlassian.plugin.osgi.spring.DefaultSpringContainerAccessor.createBean(DefaultSpringContainerAccessor.java:97)
at com.atlassian.confluence.plugin.ConfluencePluginObjectFactory.buildAction(ConfluencePluginObjectFactory.java:45)
at com.opensymphony.xwork.DefaultActionInvocation.createAction(DefaultActionInvocation.java:199)
at com.opensymphony.xwork.DefaultActionInvocation.init(DefaultActionInvocation.java:272)
at com.opensymphony.xwork.DefaultActionInvocation.<init>(DefaultActionInvocation.java:65)
at com.opensymphony.xwork.DefaultActionInvocation.<init>(DefaultActionInvocation.java:58)
at com.opensymphony.xwork.DefaultActionProxyFactory.createActionInvocation(DefaultActionProxyFactory.java:32)
at com.opensymphony.xwork.DefaultActionProxy.prepare(DefaultActionProxy.java:124)
at com.opensymphony.xwork.DefaultActionProxy.<init>(DefaultActionProxy.java:75)
at com.opensymphony.xwork.DefaultActionProxyFactory.createActionProxy(DefaultActionProxyFactory.java:43)
at com.atlassian.confluence.servlet.ConfluenceServletDispatcher.serviceAction(ConfluenceServletDispatcher.java:53)
at com.opensymphony.webwork.dispatcher.ServletDispatcher.service(ServletDispatcher.java:199)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
...
