Executors started dying on one node with unknown reason. Other nodes are not affected
According to Jenkins UI, all executors (excepting ones with a running build) continuously die and restore

• No error info even on the FINEST log level
• Executor::causeOfDeath field is null when I open the death descriptor
• causeOfDeath page is accessible, hence Executor::isAlive() returns false

Probably, a node user decreased the number of executors (to be checked)

WARNING: Caught exception evaluating: h.printThrowable(it.causeOfDeath) in /computer/XXXX/executors/4/causeOfDeath. Reason: java.lang.NullPointerException
java.lang.NullPointerException
at hudson.Functions.printThrowable(Functions.java:1184)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.commons.jexl.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:258)
at org.apache.commons.jexl.parser.ASTMethod.execute(ASTMethod.java:104)
at org.apache.commons.jexl.parser.ASTReference.execute(ASTReference.java:83)
at org.apache.commons.jexl.parser.ASTReference.value(ASTReference.java:57)
at org.apache.commons.jexl.parser.ASTReferenceExpression.value(ASTReferenceExpression.java:51)
at org.apache.commons.jexl.ExpressionImpl.evaluate(ExpressionImpl.java:80)
at hudson.ExpressionFactory2$JexlExpression.evaluate(ExpressionFactory2.java:74)
at org.apache.commons.jelly.parser.EscapingExpression.evaluate(EscapingExpression.java:24)
at org.apache.commons.jelly.impl.ExpressionScript.run(ExpressionScript.java:66)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.apache.commons.jelly.TagSupport.invokeBody(TagSupport.java:161)
at org.apache.commons.jelly.tags.core.OtherwiseTag.doTag(OtherwiseTag.java:41)
at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:269)