Do you have any security software on your machine? Or browser extensions like Ad blockers or malware protection? Sometimes these programs get things wrong and generate a false positive, meaning a legitamate site gets blocked. I’ve not seen it happen with Kirby’s panel, but I have seen them interfere with e-commerce sites, particularly when you try and pay for stuff.
Any chance you could try on another computer? The fact that it happens both on live and locally leads me to think its possibly something to do with your computer.
Are you in an office thats behind some kind of gateway, proxy or traffic filter?
If you do have such software installed, try adding your site to its whitelist. Does this happen in every browser?