Hello Bosse,
Okay, it seems like there are 2 issues here. On some posts, the "comments" are explicitly disabled. To fix this, you just need to edit the post and set "Allow Comments" to true.
Another issue is because in your settings for post options, it has been disabled explicitly. Take a look at my screen shot here,
http://take.ms/sOntz . I have turned this on and it should work fine now for some posts, example,
http://www.rolfmunke.se/bloggx/2016-01-06-07-12-55/rolfs-blogg-sa-klarar-du-festen-trots-majonaes-i-smoergastartan
By the way, I have updated the domain for you to rolfmunke.se. Please take note that you can only obtain support for this domain in the future. Should you require support for additional domains, please consider purchasing another license