Troubleshoot

Without details of the NBU issues you have, you are asking an impossible question.

If you are new to NBU you need to get on a course, and bcome familiar with at least basic config, options and features - trying to troubleshoot something you have no experience of, especially something complex like NBU is virtually impossible.

Once you have a little experience, look in the troubleshooting guide for steps on how to troubleshoot issues.

Unfortunately, without further details from yourself its difficult to give what might be classed as a reasonable answer.

One of the most important aspects of t/shooting is being able to set up the logs.  Not necessary to understaand them (others cn do that for you) but you have to be able to produce them.  See the link in my signiture to get started.