Welcome to AMD graphics! LOL
Firstly most stability issues are power related. That can mean a driver, bios or you hardware is just not giving enough power issue.
That being said this is a new architecture and maybe a future update will fix things. However RDNA/Navi has been out over a year and the complaint you are making comes in at about 10 a day on Navi still and a years worth of drivers has not removed the issue yet.
One thing I can tell you from experience in using AMD GPUs is their minimum spec for Power Supply requirement is usually way too low. Many reviewers experienced voltage spikes on these new cards that reset the protection in their power supplies. Most of them were using power supplies well above the requirement.
Your power supply while being right at the requirement many still not be enough. As they age they lose power. The more components you have the more power it uses and any overclocks in the system processor and GPU will, will pull a lot more power.
You can test to see if you are dropping below 12v with free diagnostic software OCCT from ocbase dot com. It can test all your components. You can use a secondary app like HWINFO to also monitor the power in realtime as OCCT runs its test.
If that doesn't show any issues you are at the mercy of if they ever get it fixed with a bios and or driver update.
You can then see if raising the Power Limit to its maximum of 50 helps supply a bit more power ceiling to the cards and helps stability. That setting is in Radeon Settings, Performance, then Tuning. Slide it all the way to the right.
If that doesn't help only you can decide if you want to keep the card beyond your opportunity to return it.
I know I won't ever make the mistake of keeping a card and hoping it will get fixed. I gave up on mine finally and that was a costly mistake having kept it to replace it after a nightmare of a year.
If yours is just your power supply isn't giving it enough power getting a new supply may very well give the card the power it needs. I would not go below a quality 850 though if I were you.
Luckily you already have a perfectly good card if yo decide to see if in time things improve for others. You can always buy another later on.
