I've tried to use boldbeast and other recorder with no success on this ROM with Nexus 5X and Samsung Galaxy A5 2017.
I'm rooted with MAGISK (Last Beta/Last Canary) installed callrecordingfix module and tried every Alsa settings.
Files are created but empty.
Start input is not available on A5 2017 (but is available on my Nexus 5x).
I've got same problem on both phones.