Yanmar 53 hp

I have a 2018 Hanse 455, we purchased in 2023, very low hr. only used a few weeks a year sailed and kept on the hard in the BVI. Did sea trial and inspection before purchase passed with flying colors. First day out moving to our new home a little rough 5 ft. seas about a half hour out motor quits ,  have to be towed in. Have mechanic look at engine find bad diesel fuel , clean tank clean all the lines change pre. filter and engine filter fill with new diesel. Then we do sea trial with the mechanic and after about half hour engine goes into safe mode stage 1 only allows engine to rev. to 2200 rpm. we then have a Yanmar mechanic hook computer up to the engine at a cost of $1500.00 and he could not find any problems, ran engine for about an hour at the dock. We figured we were good to go. Next day out for about half hour and engine go’s back into safe mode???? We decide to make the rest of our 2 hour trip engine ran fine but stayed in safe mode?? Next day stated the engine no safe mode took the boat out and about half hour in safe mode came back??? Dose anyone have any ideas???

Thanks Marcella, my bad I did get the code’s ,