I have one M4 phone, at first it works well, but after 2-3 months I cannot pickup my call. I restore to factory and it works well. but after 3months, cannot pickup phone again.
it is ridiculous if let me reset phone every 3 months.
3 months is a long period of time, where you can install all kinds of 3rd party applications to interfere with the calling function. Boot in safe mode and check if the same problem occurs.
