Kotis

5.3.3-7+squeeze19

version 5

No, I did not mean that. I did exactly what you describe.
Anyway, I found another older version of your plugin, from another site of ours, and copied the files into the problematic site (plugin folder), replacing the files of the latest version. This worked for me, at least partially (the graphics are not shown, but the raw data are retrieved and displayed correctly.

I’ve performed a rename of old folder, then re-installed the plugin, but it didn’t solve the problem. Any other suggestions? I run WordPress 4.5.5 running Customizr Pro (1.2.39) theme.

But if I delete and then re-install the plugin, all the past data (statistics) will be lost, right?

I have the same problem since the last WordPress security update. I guess it is something that Effect Maker developers need to solve out asap!