gigabyte gc wb867d i download crashes computer

Tried re-seating my RAM DIMM's and pressure-air-cleaning all components after re-seating them. Completely wiping my disk and re-installing Win 10. So I think all in all, the hardware should not be faulty - any crashes or at least freezes should occur while gaming otherwise, no? Only thing I did not try was try out another PSU, as the one I'm using is from my slightly older build from 2015, but still it should not be the problem as heavy gaming for a very long period of time does not cause any errors. Checked for faulty hardware (exchanged network adapter with my brother's, checked for HDD errors, ran memory check for several hours, stress tested GPU and CPU, changed some of the SATA cables). So what have I tried (this might not contain everything as I have really tried a lot and over the past few months I will surely have forgotten some things):

I went to check for any errors in the Event Viewer, but no indicators pointing to an error, just the standard 'The last system shutdown was not proper' due to unknown reasons - nothing else. So the only thing that's left is a hard reset, which is a big pain every time I have to do it. I tried waiting for the PC to become responsive after a while but after several hours, it was still the same. Using JDownloader however, I have noticed that every single time this happens, the average download speed keeps decreasing until it reaches 0 MB/s and only a 5-7 seconds after the computer becomes completely unresponsive, meaning a hard lock with no BSODS or anything - no mouse movement at all, no caps lock led working, nothing at all. Whenever I start downloading (streaming as well of course) a usually large file using either Steam or JDownloader or even Chrome sometimes, my PC starts freezing after an unexpected amount of time (I use WiFi btw). I have done lots and lots of troubleshooting and as you probably can tell - with neither luck nor success. This issue has been occurring for as long as my (semi-) new build has existed about 8 months. I have finally decided to seek technical support as this problem I have has been frustrating me for a long long time now.

Gigabyte gc wb867d i download crashes computer