works on one website but not the other

Hi,
I run 2 websites: https://www.apis.de and https://www.apis-iq.com. I have installed your plugin on https://www.apis.de and it works great. I installed it on https://www.apis-iq.com and it works badly i.e. it loads in 10 seconds and the main styles.css file doesnt load, which is the main css file for the site.
I have the same uniques theme for both websites and the same plugins installed (in fact have a couple more installed on https://www.apis.de).
Do you have any idea why it doesn’t work?