I posted another reply yesterday, but it doesn't seem to appear here. I can see it on my profile, though, so I'm not quite sure what's happening. Anyway, what I said is this:

Thanks, Russell, that was helpful. I tried a private browsing window, but it still took me back to the blog post without giving me the chance to verify. However, I realised the URL has a parameter forcing the return to the post. I removed that part, and I was able to get to the user page and verify the comment.

This seems like a bug. The URL that was emailed to me was:

https://my.remarkbox.com/join-or-log-in?email=martin%40tinlion.software&raw-otp=qUpv3IjKNr3MF9LiEI5cYohU3H79zEZn&return-to=https://devilgate.org/blog/2020/04/25/repairability-is-good/#516d23dd-8949-11ea-93a8-040140774501

And I edited it to:

https://my.remarkbox.com/join-or-log-in?email=martin%40tinlion.software&raw-otp=qUpv3IjKNr3MF9LiEI5cYohU3H79zEZn

Until I did that, I had no chance to see what username had been allocated for the test email address, so no way I can see of getting to anything useful on this site.