Ok I found a way to reproduce the issue independent of the operating system you use:
Install the Firefox extension Avast Online Security & Privacy.
Try to visit edgeryders.eu and you’ll see a similar phishing warning, coming from a check against the same Avast phishing URL database:
Indeed the same symptoms happen when visiting https://poprebel-impact.eu/ . All edgeryders.eu subdomains are affected, and that is also the reason why poprebel-impact.eu is affected, since it forwards to a live.edgeryders.eu page when visiting.
Strangely, the CNAME alias domains to which most of our edgeryder.eu subdomains forward are not blocked by Avast. For example, work.edgeryders.eu is blocked by Avast but it internally just forwards to erwork.netlify.app, which is not blocked. This proves that Avast just blocks whole domains incl. all subdomains based on a blacklisting URL database, without any check of the actual content of a page. As seen here, the exact same content can be blocked under one domain and not on others.
In the meantime I found the false positive report form of Avast and reported the issue with edgeryders.eu and its subdomains. They said they’ll notify me by e-mail once they processed the request. The poprebel-impact.eu issue will be cleared by treating the edgeryders.eu issue, due to the forwarding involved (see explanation above).
Let’s hope they are at least fast to answer at Avast. In the past, there have been many false positives for their phishing detection, and unblocking was quite painless judging from the replies in that forum.