From one day to another WP Statistics stopped counting. Uninstalling and reinstalling the plugin didn’t solve the problem. Neither did updating it to version 12.3.2.
WordPress is version 4.9.1., php version is 7.1.
No additional plugins were installed when the problem occured.
https://wordpress.org/support/topic/stats-not-updating-after-update-to-12-3/ indicates that WP Statistics might not count when a caching plugin is used. But caching is mandatory for a good performance, and performance is an important factor of the Google ranking. So every statistics plugin has to work with caching plugins.
I deactivated the plugins “WP Super Cache” and “WP Super Cache – Clear all cache”, but that didn’t change anything.
On my other websites WP Statistic works (beside the fact that it counts fantasy numbers).
As recommended on the support topic above I downgraded to version 12.2., but it didn’t solve the problem. Instead, all posts and pages became invisible in the backend views / lists “all posts” and “all pages”.
These screenshots show the problem: