macOS Server App no longer saves Websites settings I have configured about a dozen virtual sites in the Server app under Websites. It suddenly occurred that when I edit one of these websites (no matter what I edit), I click on Save and nothing happens. In the end, I have to click Cancel, and when I check back, indeed my changes have not been saved. 

Any idea why this is so and how to fix this?

I've checked the access rights in /Library/Server/Web/Config/apache2/sites, but they seem okay. Restarts didn't cure it either.

I'm running Server app 5.3.1 under macOS Sierra 10.12.6. The sites run fine.
First you should enable debug mode in Server.app by running the following command:

defaults write com.apple.ServerFoundation DebugModeEnabled YES


and restarting Server.app. This should enable the debug menu. Then make sure the "Log Actions To Server Log" item is checked. Rerun your test, and then look at the log file in ~/Library/Logs/Server.log. The file shows the request/response communications between the Server.app and the backend admin tools. Look for commands to servermgr_web, most commands are in plist format, though the web commands may be in a JSON format.

Look for writeSettings commands specifically.