I was running a version of WordPress which was too old. It was 5.0 from the debian repos.I just upgraded to 5.6 and everything is OK.
BTW, I really like your software design. Really data-driven. I’m using it for a “hobby” project which observes phishing sites. https://crimiscan.aslaets.be .
It does whois lookups, checks http status and takes screenshots and puts that in a database.
With your tool it is so good to publish that via wordpress.
Thanks and my respect.
