while serving JWT https://xxx.8083/jwtauth/conjur-jwk-set java.lang.NullPointerException/Caused: java.lang.reflect.InvocationTargetException

Question

1. Jenkins server version 2.375/2.401
2. Java 11
3. While configuration Java build hpi file and Jenkins Configuration JWT initial days working fine , but after couple of days/after couple of hours immediately through below exceptions are

Jenkins.log :

 Error while serving https://xxxx:8080/jwtauth/conjur-jwk-set
java.lang.NullPointerException
Caused: java.lang.reflect.InvocationTargetException
    at org.kohsuke.stapler.Function$MethodFunction.invoke(Function.java:401)
    at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:409)
    at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:207)
    at org.kohsuke.stapler.SelectionInterceptedFunction$Adapter.invoke(SelectionInterceptedFunction.java:36)
    at org.kohsuke.stapler.verb.HttpVerbInterceptor.invoke(HttpVerbInterceptor.java:48)
    at org.kohsuke.stapler.SelectionInterceptedFunction.bindAndInvoke(SelectionInterceptedFunction.java:26)
    at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:140)
    at org.kohsuke.stapler.MetaClass$11.doDispatch(MetaClass.java:558)
    at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:59)
    at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:762)
    at org.kohsuke.stapler.Stapler.invoke(Stapler.java:894)
    at org.kohsuke.stapler.MetaClass$9.dispatch(MetaClass.java:475)
    at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:762)
    at org.kohsuke.stapler.Stapler.invoke(Stapler.java:894)
    at org.kohsuke.stapler.Stapler.invoke(Stapler.java:690)
    at org.kohsuke.stapler.Stapler.service(Stapler.java:240)

How to fix : Null pointer exception/Caused: java.lang.reflect.InvocationTargetException without restart Jenkins server /deleted old config file.

4. what is the reason after couple of days throwing exception why not immediately?