Very strange observation regarding rendering

I have been working on rendering out a 30min fusion comp. There have been sections which would not render past about 50 seconds of video without hard crashing DR. Hard crashing as in no warning, just suddenly DR is no longer open and running. Here is what I have observed...

First, if my project setting's resolution did not match the exported video resolution, it would take absurdly long to render it. Absurdly long as in, the project setting was for 4kUHD, and the rendered segment was 2000x2000. Instead of taking about the length of the video (as it did when the project setting was temporarily changed to 2000x2000), it would take nearly 4 hours.

Second, and this one is currently in progress, the video render kept crashing DR...UNTIL...I decided (on a whim) to surf the web while DR was rendering the video. The initial attempts didn't even make it to 50 seconds before crashing DR and were showing upwards of a projected render time of 4-7 hours. Currently...while I am on youtube and typing this post...the render has reached 4:31:00 and counting...and is projecting 2.5 hours to complete the render.

Yeah...I know you're thinking it. WTH?!?!? I don't know. I always assumed operating other programs while attempting to render a video would increase the chance of crashing...and DEFINITELY increase the render. Apparently, in this instance at least, that is not the case. So, I guess I will be watching some youtube for next couple hours to make sure DR doesn't crash...and keeps those render times up??? I don't know. Maybe this is just one of those hyper-realistic dreams and I haven't been able to tell I am asleep yet.

Just an update to this weirdness. Unfortunately, no, I have not figured out any decent explanation for this high strangeness. I have tried stopping the net browser and watching what happens for short periods. The GPU ramps up usage...and concurrently, DR's projected render time starts rapidly increasing. I open the browser back up and start up another youtube video, the GPU activity drops back down and slowly the projected render time slows down and begins to decrease again. Either way, it hasn't crashed and is 96% complete. I'm just gonna keep hitting the youtube videos until it finishes, I suppose.

One more update on this odd behavior. Today, I had to fight with another section of this fusion comp. I attempted the same strategy as previously, staying active in my net browser while DR was rendering, and it crashed at around 30 seconds worth of frames into the video. On a whim, I tried the exact same render again, but went back to making sure nothing was running in the background. That time, it completed without issue. Still no idea why the difference.