You might be right, I may have described two issues, although it seems to me they are related.
1. Zoiper not woken up, which means calls return busy.
2. Zoiper woken up with delay, which means it starts ringing but the calling party has already ended the call (with busy signal). This time the RINGING packet might be sent with a delay, as elkato described.
Nonetheless, shouldn't both issues have been resolved with the new Background mode? I ran a few tests when I have the Constant Wake Lock selected. Unfortunately, it still sometimes happens Zoiper either:
1. does not ring at all and the calling party shows busy, OR
2. starts ringing with delay and the calling party shows busy.
In any case, there is definitely a difference in the delay between dialing and ringing when the device screen is on (no delay) and the screen is off (variable delay).
Could you please clarify how exactly the two new Background mode options work:
- Alarm scheduler
- Constant Wake Lock
What exactly is done in the background? What does Android do to the Zoiper app, that the background mode is supposed to fix?
Edit: just wanted to add that the issues described here DO NOT happen if I keep the screen on all the time. I actually use an app Automate to keep the device screen on constantly, and since then I encounter no issues. Of course, battery is affected, so it is not an optimal workaround.