Thanks for your suggestion.I looked at your namelist.input. There are a few concerns I have:
(1) For dx =4km, it is better to turn off the cumulus scheme, i..e,
cu_physics = 3, 0
(2) please set radt = 12, 12
(3) please change the location of your child domain. With the current settings, the child domain is too close to its parent domain. Such a configuration may lead to problems in wrf.exe run.
Please rerun this case with the above changes and let me know if you still have trouble.