Erreur de compilation Discourse : « Une erreur s'est produite lors de l'installation de rbtrace (0.5.1), et Bundler ne peut pas continuer

I’m seeing quite a few of these failing in the last few weeks, here’s another two for reference:

And three others:

Plus this actual topic, makes six that I found with just a quick search.

Can anyone spot a commonality with all of these recently-failing instances?