You should have a look at the system logs to see if there is any indication of the problem. Starting with a base system without any plugins is a good way to proceed (to rule out malfunctioning plugins).
I was getting exactly the same on a Pi Zero with 2.599. It would run for a while and then crash, either when streaming internet radio or just sitting idle. No plugins installed, just a straight fresh system burned to the uSD card. Crashed sometimes after a few minutes, sometimes stayed up for an hour or two then randomly died
Just been away for a week but before that I downgraded to 2.586 and it's still happily running (idle for the whole time, but 2.599 in a similar state would crash).
If I get chance this week I'll upgrade again to 2.599 and can try and see if the system logs have anything to say. Is there any specific way to access those, and do they survive across a crash or is there some grandfather/father/son system for accessing older logs?