Had the a couple of wires and their nuts melt down last trip on the ATS under a bunk. Was on shore power running A/C and smelled smoke and then saw it. My take on it is, and I am not an electrician, that when you have stranded wire connecting to solid wire with a wire nut, it is likely that the wire nut threads cut thru the stranded wire making for a bad connection.
MY ATF looks as if it was supplied with stranded wire pigtails that were wire nutted to the solid wires. I have since removed all the stranded wire pigtails and wired the solid wires directly to the ATS screwed connections. Sleeping much better now.
As nosticks mentioned, a close insp. of these connections should be made to look for signs of overheating and loosening.