This is in my opinion the most likely cause. 8GB of RAM is the minimum to run the NAS, and I will make an assumption here that you are doing more than a simple NAS operation. When you use more and you are using SCALE, you do not have the same feature that CORE had, the SWAP space. If you run out of RAM, you are out.
But to rule out other issues, run the two main stability tests: Memtest86+ (for 5 complete passes) and a CPU Stress Test like Prime95 for at least 4 hours. If they pass, then you have ruled out some of your components as the problem.
If you can double your RAM, you might be fine.
Your drive data looks good so I highly doubt you have a failing drive.
I agree with @kricka-kracka , I think this was a refurbished drive. They made it “like new” and sold it. It was refurbished, not new when you received it. Also, a 2 year warranty would be reasonable for a refurbished drive. This particular drive new has a 5 year warranty. You can’t trust anyone these days.
Since we have ruled out the drive as a failure, use the ZFS pages from the Drive Troubleshooting Flowcharts. You should have your system cleared of the errors quickly.