I've been playing a survival map for one year.  When the 1.16.5 update happened, I expected updates to take place on maps I hadn't explored yet.

Instead, what happened is that all of my villagers, animals (horses, llamas, cattle, sheep), maps that hung on walls (I had no copies made), and even the trails I made with my shovel (when you right-click on grass and it turns brown)—all of it disappeared.  Completely gone.  Vast roads I built are gone.  Entire villages emptied.  All horses missing.  I have no maps anymore.