The so called Net Worth report that you generate is really more like a total value of selected accounts report. Its naming is more misleading than anything. I'm not sure what you would call it. It differs from the account balances report in that the later does not include the value of securities.
I can reproduce your issue with an account that is not on the sidebar. I'm not sure if there is a solution, it appears that there needs to be something highlighted in the side bar and if the account is not present it does not seem that the highlight has anywhere to go.
Yes X in the C field indicates cleared. Reconciling in Moneydance is an intermediate stage. So there is primary two states cleared and uncleared.
Menu option Tools --> Account will give you a list of accounts and current balances. Accounts in light grey are inactive, black are active when using classic Theme (colours can vary according to the theme in use).
There are little reminders in Moneydance that accounting principles underlie the program and in some cases that the same screen is used for multiple purposes. Ideally a task should be given to a maintenance programmer to go and tidy things up.