[kbenson]

You can click the comment permalink (the age indicator) and on that page you have the option to vouch for the person /comment if it seems appropriate. I did so and they appear to be visible again. I've seen it take two vouch operations before though.

[ValentineC]

Ah, the vouch option seems to only be available on the comment permalink, and not on the general comments page. TIL, thanks!