The package repos that the importer is using are pooched. I have no specific advice on how to fix it, other than to identify which repo is providing the dud package and see if there’s another repo that isn’t broken. It’s also possible the problem is transient, and will come good in the near future.
To be honest - i’m not too good at unix-related fixes and tasks in general. I’m also not quite sure if i understand you well - is that something i can do on my own or i need to wait for some patches to the discourse repo/dockerfile/whatever ? (i could obviously do that by myself somehow but i’m affraid it’s totally beyond my imagination)
You can do it yourself if you’ve got the knowledge (or are willing to acquire it), otherwise it’ll have to wait until someone else who does have the knowledge bumps into the problem (or is pointed in the appropriate direction and told “go forth and fix”). We (CDCK) do phpBB imports every now and then, so if this is a persistent problem we’ll end up fixing it if nobody does in the meantime. It wouldn’t surprise me, though, if you try it again tomorrow sometime, if it all Just Worked, and it was a temporary repo problem.