Q:

Sometimes Apk does not install the latest code but reinstall the same apk fix problem

Currently, I'm working on a project on github and build apk then upload to google drive to deliver to my teammate.  But sometimes, my teammate install the apk and then report back to me that the apk is not latest, it shows old functions which should be removed by current. 
Here is some more informations:
What have I tried:
- Build > Rebuild Project before build the apk
- When problem happened: Close/Kill app/Clear data then reopen app does not help but uninstall and reinstall the same apk fix the problem
- Devices: Google Pixel/Pixel 3 XL  
My build.gradle
minSdkVersion 21
targetSdkVersion 29
compileSdkVersion 29
debuggable = true
sourceCompatibility JavaVersion. VERSION_1_8
targetCompatibility JavaVersion. VERSION_1_8

Android Studio version 3.4.2

Does anyone here know what the cause of this problem?  And why it happens?  Is there any way to fix it? 

A:

Ok, we found out the problem here. 
In order to test billing function, we uploaded an apk of our current app to another google play console account.  Then one of my teammate accidentally increase version code of that apk.  Now we have 2 apk stay in 2 places: 1 is latest which has lower version which I upload to drive, the other is the older apk but has higher version which is placed on google play console.  Then in my tester device, he turn on auto-update app and login into tester account (which was added as tester on console), so google play automatically "update" our app with older one. 
Anyway, thank you all for your attention.