Just received Pinephone - system crashes

[rocket2nfinity]

The bad: I realize the Manjaro software is still alpha, but I wanted to get some feedback on whether what I'm seeing is expected, or am I looking at possible hardware issues. (Is something like memtest available for diags?)

Take a look at this: https://forum.pine64.org/showthread.php?tid=9832

That thread is related to the Mobian O.S.  

I don't know if Manjaro is crashing form the same problem  ?

There is a factory test OS in the Postmarket builds that does a good job testing hardware. Many Pinephones have the dram clockspeed problem regardless of OS. Flash a lower speed and see if the problem goes away. As the builds get optimized, the problem seems to be being resolved. My phone couldn't handle more than 552, but is now running better on the latest builds. Most seem to be ok with anything between 552 and 624.

There is a memtest type setup in the thread provided.