Version 4 appears to be completely broken.
Version 4.0.6 is broken for me as well. The sitemap files are simply never created.
Reverted back to version 4.0.5 and same problem sadly. :(
Debug log shows no errors. Looks fine. And yes still no sitemap files created at all.
[autoSave:GoogleSitemapGeneratorStatus:private] => 1
[_startTime] => 1402328896.7869
[_endTime] => 1402328896.8432
[_hasChanged] => 1
[_memoryUsage] => 43778048
[_lastPost] => 109
[_lastTime] => 1402328896.8323
[_usedXml] => 1
[_xmlSuccess] => 1
[_xmlPath] => /privatePath/sitemap.xml
[_xmlUrl] => https://www.mysite.com/sitemap.xml
[_usedZip] => 1
[_zipSuccess] => 1
[_zipPath] => /privatePath/sitemap.xml.gz
[_zipUrl] => https://www.mysite.com/sitemap.xml.gz
[_googleStartTime] => 0
[_googleEndTime] => 0
[_msnStartTime] => 0
[_msnEndTime] => 0
Running on WordPress 3.9.1 with PHP 5.5. Even tried with PHP 5.4 first.
So reverted back to version 3.4.1 and working fine once again. It even correctly recreated the sitemap files as expected.
However, after I re-enabled version 3.4.1 I got these "warnings":
The last run didn't finish! Maybe you can raise the memory or time limit for PHP scripts.
The last known memory usage of the script was 41.25MB, the limit of your server is 256M.
The last known execution time of the script was 0.04 seconds, the limit of your server is 600 seconds.
So I set "Try to increase the memory limit to: 64M" and then it worked just fine, as you can see below:
Your sitemap was last built on June 9, 2014 3:48 pm.
Your sitemap (zipped) was last built on June 9, 2014 3:48 pm.
The building process took about 0.06 seconds to complete and used 41.75 MB of memory.
So then tried version 4.0.6 and 4.0.5 once again. Same problem, xml files never created.
Even tried to double memory limit to 128M to be sure.
So seems version 4 is completely broken for me.