Embedded Ecwid shop not showing until reload of page

Hey there!
Hope this is the right category for this issue:
We are using Kirby 3.9.5 with the template “zero one”. As ecommerce system we use Ecwid.
Now I tried to embed Ecwid´s shop page via integration code on our website. (Online Shop | Schnick Systemtechnik)
Unfortunately on most systems I tested this on the shop page only shows after refresh. Same issue with ecwid´s buy-button. Some colleagues told me that it worked fine for them… I found no correlations; tested different browsers, OSs and security setups.

I´m stuck here and have not idea what might cause this. Can anyone give me a hint?

I have no experience whatsoever with Ecwid. What I do see when visiting the site with the network tab open is that the server response is very slow, maybe that causes those issues.

first time I opened your link, the shop was there, but navigating back and forth, it disappeared again.

When integrating the stolen code from your site in my local Starterkit, it works without issues…

OK, thanks a lot!
Then I will try to reduce the image size or something like that.

Is there a possibility to implement a “wait” command in a code block to keep the server connection open long enough to fetch all needed data?