PBO is by AMD's definition considered an overclock but IMHO really is not. PBO only makes the boost algorithm already built into Ryzen more aggressive. It doesn't increase the speed you can boost to.
What you may have is a cpu that barely made the validation to be a 3600 chip and turning on PBO makes it unstable. It can also be that turning on PBO brings out flaws in other components like memory chips that are not at correct timings, are bad or are not on the boards QVL list.
PBO will actually make the CPU use a little bit more power. In your case your GPU is already using a Power Supply that is minimum spec for that card. So a little more power may be pushing that over the systems stability edge.
You could RMA that chip with AMD, just don't tell them you used PBO as it does void your warranty.
Before doing that try a few things.
Reset the bios to defaults.
Run one stick of memory at a time and see if one is more stable vs the other. Also make sure the timings are being applied correctly. If your memory is not validated for your board then it may not be setting the timing right requiring you to do this manually.
Test your Power Supply with OCCT from ocbase_com. See if that finds any physical problems with the CPU. You do have a quality power supply so likely it isn't a power supply issue but always worth checking.