After some tries and fails and research, I've figured out that what was happening was that a font that I was using didn't get transfered to the assets for some reason, after uploading it back the apk is working fine.
If someone else finds trouble on this matter:
To figure out what the error was I used the adb cmd tool from android sdk, I followed this tutorial from @Taifun:
adb logcat | findstr "your package"
"your package" being for example appinventor.ai_username.appname