loads error

Do you have the opportunity to test the site offline? For example using Wamp?

sure, but by xampp ??

Thanks!
Maybe the problem is due to your server. Perhaps with Xampp the error does not recur.

unfortunately, same situation on offline xampp server ??

Test with another theme, like the WordPress default.

tested on twenty twelwe and twenty fourteen still nothing changed ??
https://betatest.heliohost.org/wordpress/?p=4

you got some site where it is working?

someone got the same error like me
https://www.ads-software.com/support/view/plugin-reviews/fl3r-feelbox?filter=3

You can see for example https://labottegadelmistero.altervista.org

I patched the error, now you can try to download the 3.3 version.
This version corrects an error found in new installations that did not allow you to use the plugin: during installation were not created tables in the database. The error is not reported if you have installed the plug-in versions prior to 3.0.

Tell me if you can solve the problem by downloading the new version.

An example is

Try with the new version 3.3.1, it may patch the error.
The error is due to the fact that the plugin did not create tables when installed, and affects versions 3.0, 3.1 and 3.2 (as far as I could understand). Update at 3.3.1. and if this is not enough, try to delete the plugin from the WordPress control panel, reinstall it, write a new post and try it.