It runs normally with gasoline ( E20 ). But only short time with CNG. Motor suddenly stops and does not start again. Yellow motor warning sign is lit.

Car can be started again after taking CNG controller fuses out. It will run normally as gasoline only mode. It is also possible to use CNG again ( for short time ) by placing the two CNG related fuses back again. Car stops again after a while and then have to take out those fuses again.

Car is about three years old, about 35000km. Car has been serviced in Toyota service center. No CNG parts or filters have been changed yet. Toyota insists they can not see anything on their computer when connected to car computer. Toyota service wants to replace CNG controller, they did not say why but insist to replace it. It looks like they just try to change parts one by one and see if it helps.

Is there good quality CNG specialist service place in Pattaya Jomtien area?

Where could I buy adapter for car computer ( usually they are USB devices ).

Anyway I learned that if you start to have trouble with Toyota Corollas CNG system you can "modify" it back to gasoline only by taking out two fuses ( CNG ECU1, CNG ECU 2 ). Both are 20A fuses.

Sounds like the CNG controller to me, nothing else it really can be, definitely electrical in nature. CNG valves not getting proper impulse from the engine and electronics, you are resetting to default when you disconnect power and it works temp until the internal fault shows up again after it goes through diagnostic mode, safety is high priority with gas systems. It could possibly be a faulty injector throwing it into fault mode but really hard to tell, I'd start with the controller, do they have one for testing?