cannot write to .htaccess & does not allow visual appearance change

First – I ran through your must dos before writing this.

The second issue started with the 4.7 upgrade and I have run through all permutations since then to fix the issue with each upgrade to 4.7.2. No matter what, since the 4.7 upgrade, when I go to Appearance: Customize, I get the left navigation of the customize screen but where the page should be to visually view changes it says “Non-existent changeset UUID.” I have heard mention something about it having to do with the fact my WordPress Address (URL) & my Site Address (URL) being different, but since that wasn’t a problem BEFORE 4.7, it has to be a 4.7 issue.

Now. just today as I was checking it again after the newest 4.7.2 update, I found an odd error in the permalinks settings. (I have no idea when it started as I hadn’t looked at the permalinks page in a very long time.) It tells me it cannot write to the .htaccess file and so I need to put in the WP code. I looked up the information on your site to make sure that was right. It was, apparently, so I tried several things.

1. I tried changing the permissions on my .htaccess file. No matter what permissions I gave it – everything from 644 to 777, the WP admin still told me it did not have access.

2. So I changed the htaccess file myself. It still gave me the ‘you need to update the .htaccess file’ error.

3. I checked the .htaccess files on the rest of my WP installations and they all have 644 and work just fine.

I have no idea if such different problems are somehow hooked to the same issue, but the one WP installation that has problems IS the one with a different WordPress Address (URL) & Site Address (URL).