Echo occurring when creating multicam video with multi audio

I hope someone can help with this issue its very frustrating.

I am using two camera's and 3 audio devices - lav mic, shot gun and dynamic mic - all connected to zoom h6 recording device and all recording at the exact same time. The purpose of the recording is for an interview.

I select all video and audio files in the browser and create a multicam clip, relying on audio syn from the camera mic. For some reason I get a very slight echo from the lav mic but the other mics are ok.

Now, this is the bazaar part, if I drag just the audio clips into the timeline there is NO echo and I don't have to make any special adjustments to the audio tracks to get rid of echo. It just works fine. I can then create a compound clip with all 3 audio with obviously no echo. It is only when I create a multicam clip that the slight echo occurs, which makes no sense to me.

All this would be ok if I was able to create a multicam clip with just the video and create a compound clip with the audio and then somehow edit them together but as far as I know this can't be done.

I'm hoping I don't need to take the audio into another audio program and create one wave file then bring it back into fcpx and then create a multicam clip. And I'm not sure how to make audio syn better once the a multicam clip has been created, which I don't actually think is the issue anyway.

Has anyone else had this issue, I hope you can help.

Hi Knight, Welcome to the forums!
Lav mics can create echoes. The pick up patterns are typically omni directional, and they can pick up sound bouncing off of reflective surfaces. So I am not surprised that you notice it from the lav mic in particular.
It can also be a problem when 2 or more talents have lav mics on and you get a double recording with a slight delay from the other speakers voice.
I am somewhat more puzzled by not having an echo for audio only compound clips.
Are you sure that you are muting the audio from the on board camera audio?
Since you are using separate audio recordings, make sure to use your best sounding audio for each clip and attenuate all other sources.
You can also create separate "angles" for each audio and select audio in the angle viewer or lock the audio to just the best audio angle.
Hope this helps, Greg