Hi Pete,

For the first question, what is the condition that you want to show for showing the bank account? If it is simply the debit/credit condition of the bank account for a specific column, it doesn't matter whether any of the other column values are:
=IF($D6=0,"FormatHidden","") goes in the RowFormat column.
=ADDEBIT and =ADCREDIT is used for outputting the bank amount.
If using a SmartSheet, you should separate the bank account out from the other accounts and be on a separate row.
A sample spec GL!BankLOC shows formulas.

If you want to have different hiding results of row based on 'mixed results', then you need to consider what conditions force a row to be hidden. Perhaps all columns need to be credits (or debits) in order to be hidden. Remember, you don't want the bank account to be showing in both or neither of Assets/Liabilities.

When doing formulas with FormatHidden, it is best to not have .RowFormat in the top corner until you are sure things are working. You can tell if a row will be hidden by seeing 'FormatHidden' in the right-most column.
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As for your second question, the scenario is likely that a row has been interpreted as having zero height, rather than being 'hidden'. The likely solution is to highlight the rows above and below the missing row, then re-size any of the visible rows. This will force a resize of all rows to match, including the missing ones.
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There are a couple of FormatHidden issues not hiding/showing correctly that should be resolved in the next release of Ledger. These changes have already made it into the FX80G release.