Thank you for contacting us and sorry to learn about the issue with the nested view.
The main challenge here is that the blocks based views don't support the nested views, as we discussed in the other ticket. Whenever nested views are involved, our recommendation is to use the views created using the classic editor.
I tried to access the admin area, but it seems that the default admin login link has been changed on your website. I'm setting your next reply as private so that you can share the admin login link too.
After testing a couple of different approaches, this is the solution that works without any consistency issues.
Instead of processing the view's shortcode "[wpv-view name="view-to-show-les-avis-related-to-entreprises" wpvrelatedto="[wpv-post-id]"]" inside the content template for single "Villes" post, I registered a custom shortcode and that processes the same and returns it output:
( shortcodes within shortcodes are not very well supported in blocks/Gutenberg editor )
After that, I've inserted this newly registered shortcode in the content template for the single "Villes" post and it keeps working, without any interruptions.
( screenshot: hidden link )
As for the "processing server request, please wait ..." message, it is showing in abnormal frequency on your website, when the content template edit screen is open.
To troubleshoot this behavior, you can test it with all non-Toolset plugins disabled and a default theme like Twenty Twenty.
If it's fixed, you can start adding the disabled items, one-by-one, to narrow down to a possible conflicting item.
I hope this helps and please let me know if you need any further assistance around this.