Hello everyone. 

I found a problem when I want to add text. The overlapping texts seem to create a hole in the text. I have tried changing the font types but the text still appears to be like the pic I attached below. And when I export the text, the result looks exactly looking like that.

How can I remove the missing part of the overlapping text? Thank you very much.

I'd try setting the fill-rule:

Ah thank you very much for the help, it worked!