Plugin loading but no display

Hello,
I’ve been using this plugin for a long time now, but it just appears that it’s not working anymore. When I try accessing the plugin, it keeps loading and I see this:
https://ibb.co/qs75NrT

I went to support and it keeps loding for this:
REST API:
Testing – 0%

When I refresh the page I have the classic red box telling me that “error: networkerror when attempting to fetch ressource”

I tried to deactivate the main optimization/cache plugins but still I see this error.
What are the next steps?

Thank you very much,
Michael