The photos wouldn't load in my post, so I've added them in this comment.

And yes their sideways. But not on my iPad. IDK

Cut into the wood to see if it is still alive. I'd dig it up and look at the roots.
You may have nematodes or crown rot

You need to do a search for nematodes and crown rot, and that will tell
you everything you need to know.

A possibility also, it might have had too much water or water logged..fruit trees don't like wet feet, make sure drainage is good.

Lack of drainage is one of the biggest problems with growing stone fruits along the coastal area. I plant all my peaches and plums in raised beds. If you dig a trench to drain the surface water it will help. But if the soil stays saturated for long periods of time, the roots cannot get oxygen and will rot. That is true even in winter.