My armor still reads a 0 in its armor rating, I can still wear it over other pieces
It is still INVISIBLE

Anyone have release notes?

Can you try saving an ESP that was not already broken with 1.6.91 using 1.6.89 and see if it works? Have you only tried to save an .ESP that was previously broken with 1.6.91?

A new Skyrim 1.6.91 version could fix your mod, but a CK downgrade to 1.6.89 won't. Youll need to fix it one by one (or wait for the next update, but maybe they finally decide to not include the changes introduced in 1.6.91, so, I wouldn't do it).

From what I understand, nothing can fix a mod already saved in .91 (Except maybe Skyrim version .91). However a save from before 91 will work just fine. If you can revert conveniently (I only lost like 4 hours of work), do it. Otherwise you may have unforseen issues.