I got the same flood of errors on Jenkins 2.263.1
WARNING h.s.HttpSessionContextIntegrationFilter2#hasInvalidSessionSeed: Encountered IllegalStateException trying to get a user. System init may not have completed yet. Invalidating user session.
Took a look at jenkins.wrapper.log and noticed
2021-01-11 00:37:42,243 FATAL - WMI Operation failure: AccessDenied
at WMI.WmiRoot.BaseHandler.CheckError(ManagementBaseObject result)
at WMI.WmiRoot.InstanceHandler.Invoke(Object proxy, MethodInfo method, Object arguments)
at winsw.WrapperService.<Run>g__Restart|33_5(<>c__DisplayClass33_0& )
at winsw.WrapperService.Run(String _args, ServiceDescriptor descriptor)
at winsw.WrapperService.Main(String args)
So it looks like the Web UI /restart endpoint is trying to actually restart a Windows service, for which it does not have permissions if running as a limited user. To fix this, it is possible to run Jenkins as a member of Power Users or Administrators group, but I chose to grant permissions for restarting only the Jenkins service.
Using setacl, to view permissions:
SetACL.exe -on jenkins -ot srv -actn list
To grant service restart permissions ('jenkins' is the name of the service and 'domain\user' should be replaced with actual values):
SetACL.exe -on jenkins -ot srv -actn ace -ace "n:domain\user;p:start_stop;m:grant"
Tried it, and it worked for me.