The four pan rule is real but it's not really about the pan count itself. What actually matters is airflow and how full the pans are, because a shallow pan of chicken stacked six high won't leak if nothing is pressing on it. The problem in your story sounds more like a bad seal or a pan filled too close to the rim, not the stacking height alone. So Ray's advice worked for you, but the real rule is never fill anything more than two thirds up and always check for dents in the pan edges before it goes in. Stack height is just the easy thing to point at when it all goes wrong.

That "47 marks on the lid with a Sharpie" thing is the real story here, because tracking it was the only reason you caught how fast it went. That wire cooked black right at the heating plate tells you everything, they use the thinnest gauge wire they can get away with and it's the heat cycling that kills it, not the number of uses. So every batch puts a little more stress on that one weak spot until the metal finally gives. Here's the part that gets me though, if you'd hit 46 or 48 you'd never have noticed, you'd have just tossed it and moved on like everyone else. The round number is a coincidence, but the dead wire at 47 uses is a design choice, somebody ran the math and figured the thing only needs to outlive the warranty. I'd bet real money that same cooker dies somewhere between 40 and 60 for almost everybody who owns one, they just never keep score. You basically ran a free test on a Walmart rice cooker and the results are exactly as sad as you'd guess.