Some phones have an option that automatically closes all apps when phone is on sleep mode. This prevents ACR from starting and recording when there is a call.
In order to avoid this issue, enable ACR notification and then find the power saving option on your phone, open it and add ACR to protected apps or disable optimization for ACR. It is usually under Phone battery settings.
This option might be called:
- "Power saving"
- "Batter optimization"
- "Battery usage"
- "App optimization"
Here are the screen shots from different phones showing power saving setting
Some Android 8 Phones
OnePlus and Huwei Android 8 updates have bugs that puts apps to sleep even if they have on going notification. Try disabling battery saving mode for ACR if you experience such issue.