My guess would be that on a cold boot the fan is running slowly or starting slowly or even possibly not starting up immediately. That would give the intermittent error you see. When you run diagnostics is it from a cold boot or after the system has been on for a while (a restart)? If you call Dell tech support they will probably run diagnostics and find no problems either but it may be worth a call. Short term keep an eye on it as it will probably become more troublesome if the fan has a problem.
I've had my Dell Inspiron 16 plus for less than a week now. When I power it, the preboot check says fan malfunction with error code 2000-0712. The solution suggested was to check for any obstruction in air vents and update BIOS. Air vents are open and I updated the BIOS. I ran dell hardware diagnostics from the boot menu and it says no issue with the hardware. But I keep getting this error. The laptop is not overheating. It's a bit warm on the bottom side. No heating issues when I play games. I ran stress tests for CPU, both intel integrated and Nvidia GPU. Tests came fine and no overheating.Also, I only get the error when I shut down the laptop and switch it on. The error won't show when I restart.
Getting error 2000-0712 when powered on but shows no issue in Dell diagnostics