When you say "missing holdings", what exactly is happening?
Has the Transaction List (register) been replaced by a dashboard with 4 big squares, or if you click on the Holdings button are some or all of the securites in the account missing, or is it something else?
OK, thanks for clarifying.
In the Holdings view, if you change the As of date to go back in time, is there a date when the missing securities reappear? If so, are there any transactions - Sold, Removed, or a Placeholder for example, that would remove them from your account?
Did the bonds mature?
Have the missing securities been replaced by something else - cash or different securities for example?
If you go to Edit > Preferences > Investing, is the Show hidden transactions box checked? A hidden Placeholder might explain the disappearance.