@movq I noticed that:

gopher://uninformativ.de/0/phlog/2018/2018-06/2018-06-01.txt

Is the first non-justified, and it is when you started using Markdown. The last justified one was:

gopher://uninformativ.de/0/phlog/2018/2018-05/2018-05-27.txt

So, I might have found the mystery! :-D