Was working – suddenly stopped

This excellent plugin has worked fine until recently. However, the mobile images are no longer being served and full size images are being used. The adaptive-images directory exists (I can see it on the server) but stopped adding new images in April. The DEBUG says the image cache directory has not been created. When I put the path to the directory manually into settings and save it goes blank and does not show the path.

Advice needed, Many thanks.

DEBUG INFO

? PHP GD library is installed.

? Image cache directory has not been created.

But this is probably because the cache has not been accessed yet.
After accessing your website from a mobile device the directory should be automatically created.

. => drwxr-xr-x

? Installation .htaccess file is setup OK.

/home/navylook/public_html/.htaccess => -rw-r--r--

? Adaptive images settings dump:

array(14) {
  ["resolutions"]=>
  array(3) {
    [0]=>
    int(1024)
    [1]=>
    int(640)
    [2]=>
    int(480)
  }
  ["landscape"]=>
  bool(true)
  ["cache-directory"]=>
  string(0) ""
  ["watched-directories"]=>
  array(2) {
    [0]=>
    string(18) "wp-content/uploads"
    [1]=>
    string(17) "wp-content/themes"
  }
  ["jpeg-quality"]=>
  int(45)
  ["sharpen-images"]=>
  bool(true)
  ["watch-cache"]=>
  bool(true)
  ["browser-cache"]=>
  float(7)
  ["hidpi"]=>
  bool(false)
  ["cdn-support"]=>
  bool(false)
  ["version"]=>
  string(6) "0.6.70"
  ["sanitized"]=>
  bool(true)
  ["wp-content-dir"]=>
  string(37) "/home/navylook/public_html/wp-content"
  ["wp-content-url"]=>
  string(38) "https://www.navylookout.com/wp-content"
}

The page I need help with: [log in to see the link]