Hi I bought Spark in Japan and was using RC in Japan without any problem.
Last week I brought it to Thailand and tried to fly  using RC but unable to connect to spark. Does anyone encounter same problem? Does anyone know why I couldn't connect?
I managed connect with phone to spark.
All the applications were updated

Just to verify, have you tried to reset the RC or relink the drone and RC at that time? Please first trying to reset the RC by pressing and hold the power button for 9 seconds, and then try to relink the drone and RC. You can refer to the tutorial below:
Please pay attention to the RC indicator, if the RC is blinking twice a time even after 1 minute, it might need to be sent in for repair.

I didn't reset RC at that time. But reset spark( pressed for 9sec till reset for reconnection)
Now I'm back in Japan and connected without doing anything.
Can I understand that whenever you go different country. I need to reset RC side , not spark?