First of all, you NEED to get rid of that Masterwatt Lite 600w unit. Possibly one of the absolutel worst power supplies I've seen from a major brand in the last ten years. It certainly has one of the absolute worst review scores on JonnyGuru for a major industry player that I've seen aside from maybe Raidmax or Aerocool. Well, actually you can include some of the Thermaltake units with those as well. Pretty bad either way.
www.jonnyguru.com
I'd recommend, highly recommend, that you seek out a quality 550-650w unit.
Below you will find MY standard list of recommended power supplies and beyond that this thread is intended as a landing place for questions or discussions regarding specific units, platforms or related PSU tech, all of which are all welcome to be discussed here. If it's related to power supplies...
forums.tomshardware.com
Chances are good that just doing that may resolve all your issues. For real.
Beyond that, I would make CERTAIN that you have the absolute latest motherboard BIOS version installed. If you do NOT have the latest BIOS version installed, be SURE to read ALL of the notes on the BIOS update page because there are some prerequisites you need to follow such as first updating to specific versions and updating the chipset drivers to those currently available from the AMD website for many of these updates. It would be good to simply report back here with WHICH BIOS version you DO currently have installed, and we could go from there if necessary.
Also, make sure you have the latest chipset drivers installed, located here:
https://www.amd.com/en/support/chipsets/amd-socket-am4/b450
But deal with the PSU before doing ANY of that. Random shut downs don't generally happen unless there is a serious motherboard problem or a bad PSU, or a short somewhere, and given the model of that PSU plus the nature of your hardware, it's not hard to see that the problem leads directly to that poor quality power supply.