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 which was formatted differently than it is 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. the page would load if the post was flagged as spam/offensive.
The fix that was applied reformatted the old data so that we no longer need to be concerned with special handling, hopefully preventing headaches like this in the future.