No mine was a iPhone XR. My box only came with a lightening cable. Although I think they now ship them with both leads.
Hey did you have any luck ? I am having the same issues as you are for a while now but havent been able to find a solution on the internet yet 
Did the change to WAV work for you ?
I thought maybe it happens when I use the phone to check the time or anything while recording but it seems pretty random to me.
Hey. No, changing the settings to WAV made no difference - I still got the random distortion. I even tried without touching the phone during the whole recording process.
I ended up selling my evermix box in the end and just resorted back to using audacity on my lap top.