Sony A7IV Audio Problem with Sony ECM-B1M

[barryokebarry]

Hi, i'm really hoping someone can help me. I have a Sony A7IV camera and have bought a ECM-B1M microphone for it, it sounds amazing 90% of the time, however 1 in say 20 / 30 clips (approx 30 seconds long each) bypasses the Sony ECM-B1M microphone and records using the internal microphone (very poor audio).

I've updated the firmware for the camera before using the mic and it just happens out of my control, sound levels look normal, then when I check the footage, it's gone. I make videos for a living with these cameras so it's important the audio is consistent for my clients and the worst thing is this is the 3rd ECM-B1M microphone i've tried to try and isolate the problem but all 3 of them have had the same problem. 

I have done some searching but couldn't find anyone else with a similar problem so am really hoping someone has heard of this before or has some suggestions. 

[danardeng]

The ECM-B1M work with multi interface shoe.

Are you confident that the contacts of your hot shoe are clean and without oxide?
Is the lock well closed?
Can you associate the issue with the low level of the battery?