Well, it's so weird. This is my own server, and I created a VM with Ubuntu specifically for this test installation (twice, indeed, to discard if it was a VM problem).
We are migrating to my own server. The production environment is using another host, but it's a bare metal plan with a different distro and PHP version. So in the past, I've installed this software several times, and this is the first time I've encountered a problem like this. 😥