If that footprint at PCB has not set its connection to Solid, or zone has not it set to Solid than you should set ‘Solid’ for all 8 vias and for thermal pads, I think.
Thermal pad is the metal at bottom of IC. Its purpose is to allow for heat transmission from internal IC structure to PCB.
Thank you all. Finally i get it working. I changed the footprint with a different one which has a thermal pad included and routed that to gnd and it works.
Meh, you’re taking shortcuts.
If you want to understand KiCad better, then compare the differences and learn from why your own footprint does not work properly.
It’s probably something simple such as the diffence between pad Nr 9 and pin numbers “10” for the via’s.
In this instance… Forgetting to indicate which vias need to be tented to the fabricator - it would have only been one side
The usual reason I am given not to tent both sides is the pocket of air that can pop under reflow
I have only once (several years ago) heard about that problem and now I realized - I have completely forgotten it. Our contract manufacturer never complained on it.
Looking closer to one my assembled PCB I think I know why. I use 0.7 and 0.5mm vias end even they are nominally covered by solder-mask they are really opened - too big to be closed with solder mask. At that PCB I have six 0.3mm vias at one thermal pad so one side is not covered, and I see that second is not plugged by mask (also too big to pe plugged) so you can expect wicking.
I don’t have a microscope, but using lamp with magnifying glass + hand magnifier I don’t see tin at least half way deep (1.5mm PCB).
May be the wicking problem was bigger with Pb soldering. I think PbFree solder has lower wetting capability.
Thanks. I hope I will not forgot once more about that problem, but fortunately I can don’t care of it now 
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