Seems I am not the only person with this issues nor is this a problem new to 2.8.4. My tags and categories and blog links are gone. They still exist somewhere in my database however. I am not a wiz at this stuff and it can be really hard. For the moment I am not getting much help from the tech guy at my hosting service and maybe that will change if I can get someone else.
If I try to add an old category I get a 'category already exists' type message. Tag cloud still shows but cannot add new tags in post edit section. All posts show as 'uncategorized'. For a couple days everything was normal, I did nothing, and then it all vanished again. There are lots of posts here on the problem, many going back to 2.6, but no real solution. I tried using my provider to restore previous settings but that did not work for certain reasons.
Any clue what this is all about? What has been done before? Will the matter be okay after 2.8.5 (of course no one can know this for sure, but wonder if upgrades in the past have helped).
Does not seem there is much I can do.