I was sent here as suggestion from #C081AF4JK70. To quote: "Please also ask in #C19FD9681 - maybe someone from the community can help"
Also, I know I'm using the plugin correctly as it used to work previously, and downloading the signatures shows that they should be signed correctly.
Aside from that, perhaps someone could suggest an alternative to the current plugin I use or has run into the same issue and can provide a solution.