Thank you all for reporting and excellent documentation of this issue! We have applied a fix and all the affected pages should now load as expected for logged in users as well as anonymous users.

As you all observed, the issue was indeed linked to older pre-migration post history deletion data being in a different format than it is currently structured today. Some code was released recently which did not handle the old history format, resulting in the error. This impacted both questions and answers but only in some conditions as you identified, i.e. post was not flagged as spam/offensive. 

The fix that was applied was to reformat the data so that we no longer need to be concerned with the special handling of old data, hopefully preventing headaches like this in the future.