Only two testimonials appear, and then they disappear

Hello all, great extension, even if I have an issue with it.
I've configured 4 testimonials, in the slider 2 columns mode, but only two testimonials appear, and then they disappear to the top. The other 2 testimonials never appear.
What could be the issue ?

Please see it here www.elementotango.it

Many thanks for your help!

Kind Regards Andrea.

Hi, any news or hope to resolve my issue ?

Thanks in advance!

Regards Andrea.