asynchronous functions with "Contacts" plugin

Hello,

I have 2 buttons on my HTML project. I am also using Cordova-plugin-contacts.

By clicking 1st button, I am reading firebase database (with "once" method) then using navigator.contacts.find. 

By clicking 2nd button, I am reading firebase database (with "once" method).

These two buttons are working fine individully (even clicking multiple times). However, when I click button 2 after button 1, I could not able to read database.

I have lots of "database read" operation with no issue until I have started to use navigator.contacts.find Do you think there is a relation between these 2 functions(database read and navigator.contacts.find)?