sometimes paste doesn't work

environment: windows 10, openjdk 1.8.0, sikulix1.1.1
I wrote a python file. Here is a part of code:
     1: click(.ping)
     2: wait(1)
     3: paste("A")
     4: wait(1)
     5: type(Key.TAB)
     6:wait(1)
     7:paste("B")

I try to input datas on the web site.
When I run it, sometimes paste doesn't work.
sometimes paste("A") successes but sometimes fails,
and, sometimes most of pastes successes but sometimes most of pastes fails.
I want paste to success all times.

Could you tell me how to solve this problem.

thank you very much for your helping.