For what it is worth, I had a Switch (water damaged) showing this exact behaviour. Patched, booting to AutoRCM, no shorts anywhere.
In the end I went round cleaning absolutely everything with a dental pick, contact cleaner, IPA, wire brush. And reflowed all the chips I could (MT, BQ, Audio, MAX etc etc.), basically any area that shows some corrosion but the cleaning wasn’t getting too got reflowed with the exception of the SoC and RAM, which I considered too risky.
To my surprise, it booted right up.