Hello @MesmeR
The Event 3213 refers to a failure to initialize a program due to a not ready network. Details: Initialization failed because network %1 was not started.
In the error you have recorded the process ID of the Application that suffered the error (in this case <Execution ProcessID="4") that you can check from Task Manager in the Details tab under the columBe aware that PID will change every time you reboot the computer, so you should check the Process during same Windows session.
About the restarts when running on idle or low usage, it may indicate some voltage issue. Do you have any custom setings on your BIOS like overclocking or so? The recommendation would be to set everything to default (or Optimized settings) and Disable XMP profile for RAM as test measure. Furthermore, I would recommend you to open a question to the motherboard manufacturer forums, as their community would be better equipped into hardware testing, BIOS configurations, motherboard voltages, etc... since likely this doesn't sound like a Windows related issue.
Hope this helps with your query,
-----------
--If the reply is helpful, please Upvote and Accept as answer--