Why are Vietnamese Restaurant workers in Berlin so unfriendly?

So, first of all I love Vietnamese cuisine and it's in my Top 5 of best national dishes... But there is just one big thing what bothers me.

Anytime I go to dine in a vietnamese restaurant the workers are totally unfriendly and always give me the feeling of being a burden to them. I tried several many viet restaurants and it's always the same experience. Idk if it has something to do with the language barriere bc 90 percent of the waiters cannot communicate in German but it's never a good experience for me.

I just want to have a nice time, I always tip good but whatever I do to break the ice it's always the same mean face.

This makes me extremely insecure visiting a vietnamese restaurant. It's a very humbling experience,lol.

And please don't tell it's the Berlin way. I am a Berliner myself.

Am I paranoid or did anyone of you gone through the same?

Edit: I want to clear that I'm not racist. I just shared an experience what bothers me for a long time, because many Vietnamese I met at work where the most kind and sweetest people in the world. But if I visit a vietnamese restaurant it's always a unfriendly or passive aggressive encounter.