Customizer funktioniert nicht

Ich habe heute zum ersten Mal ein Template auf Joomlaplates-Webseite runtergeladen.
Habe aktuellste Firefox Version, aktuellste Joomla 3.9 Version und PHP 7.3.
Template konnte ich problemlos installieren, aber der Customizer des Templates (Modern) funktioniert nicht (wird nur Symbol für Laden des Customizers angezeigt).
Muss noch etwas installiert sein, oder was sind die Mindestvoraussetzungen?
Warp Info:
System Check
Warp engine operational and ready for take off.

Hallo, bitte lesen. Denn es kann viele Ursachen haben
yootheme.com/support/question/75099

Hello,
I have problem by template MODERN. The customiser is not loading see the printscreen. How can I solve the problem?
Thank you

I tryed instal template TRAVEL and with this template I dont have problem. I think, that is some error in instalation file quickstart by template MODERN. Please can you check?

Hello,
please check if the system output is disabled. Hide system output must be disabled to see the customizer.
And delete all layouts you dont need.
See image

I used setup by "hide system output" see the printscreen, but customizer still not working. I also try to use all tips from yootheme.com/support/question/75099 but customizer still not working. I use instal other template "GOLF" and I have same problem. But for example by teplate "FAGO" I dont have this problem. In FAGO customizer working correctly. I think, that is some error in instalation files by teplate MODERN and GOLF. Please can you check this and can you give some other tips, how the solve the problem.

Thank you.