Yanmar 6LY lost oil pressure

I just had a problem with one of my yanmar engines. The boat is a 2004 Luhrs with two 6ly2a-stp engines (could be a different 6LY - turbo, mechanical fuel injection, and 440hp). One of the engines lost oil pressure and still ran fine. Thinking the gauge/sender was bad the engine was still used until about two hours later. It was shutdown after starting to pop and make other awful noises. Any idea why this engine would lose oil pressure? The oil was checked when it first lost pressure and it was full. Checked after being shut down and it was still full. No leaks in the bilge. New oil and filters only 1.5 years earlier - maybe 50 hours prior. Do these engines have problems with the oil pump? blockage in the oil gallery? pickup being blocked?

Any possibility these engines come with a warranty?

Any help is greatly appreciated.