Lightroom: Local moire edits not visible in Library

Try the edits on a Virtual Copy and see what happens. Try using the brush on a different image and see if the same thing happens. Try other edits too and see if they appear.

The problem of brush-edits not being saved has never happened before. Other brushes, like exposure, work fine. No difference with a virtual copy

Your edits aren't "gone", it sounds like they're just not being displayed as you might expect in the preview used by the Library module.

There's been a lot written about it in the past, so I won't rehash things here, but the previews you see in Library & Develop are actually different.  They can use different color spaces, different resolutions depending on your settings, etc.  The only true representation of your image with your Lr adjustments applied is the 1:1 preview in Develop.  These articles aren't specifically addressing moire, but they may help you understand the different previews Lr uses -

http://www.lightroomqueen.com/lightroom-performance-previews-caches/
http://asktimgrey.com/2015/04/22/blurry-preview/

Outside of that, what preview settings are you currently using?  You can check them by going to Catalog Settings -- File Handling tab -- and look at Standard Preview Size and Preview Quality settings.

In Library, if you zoom in 1:1 in Loupe view, is the moire pattern visible?  (I'm assuming you're using the adjustment brush to reduce moire.)