render_list does not render tiles for bigger zoom then 6

render_list --all -n 5 --min-zoom=0 --max-zoom=9 render_list -a -Z 16 -n 5 Both give me

Rendering client
Starting 5 rendering threads
Rendering all tiles from zoom 0 to zoom 16
Rendering all tiles for zoom 0 from (0, 0) to (0, 0)
Rendering all tiles for zoom 1 from (0, 0) to (1, 1)
Rendering all tiles for zoom 2 from (0, 0) to (3, 3)
Rendering all tiles for zoom 3 from (0, 0) to (7, 7)
Rendering all tiles for zoom 4 from (0, 0) to (15, 15)
Rendering all tiles for zoom 5 from (0, 0) to (31, 31)
Rendering all tiles for zoom 6 from (0, 0) to (63, 63)

and then it just stops. Left it for a couple of hours - nothing changed. CPU is loaded by 20% with x-org and gnome-shell. What might be the problem?