sitemap.xml is empty or crashes

[DaltonDev]

When creating a new sitemap I have tried everything (that I can think of) but I cant get this to work. I can see the sitemap just fine when I view it from the Admin GUI, but whenever I go to the url ../sitemap.xml it either crashes or is empty.
This is my setup (Cant use root -1 because there is to many entries):

Running the scheduled job (i've tried many different root pages)

When going to sitemap url:

Viewing the same sitemap through Admin GUI everything works

When setting debug to true I get this error (and occasionally some error about unclosed comment):

When I set debug to false it shows nothing, and the file when downloaded is empty.
Sitemap.xml (228kb) is the one were debug is true and it crashes with error about unclosed comment and Sitemap2.xml (0kb) is with the same root but with debug false.

What am I missing?