AE is stealing focus after rendering finishes

THIS!

Incredibly frustrating and honestly just feels like Adobe is being rude every time it happens. Feels like someone slapping you in the face when you're working hard on something. 

YES i know your app has just finished doing something, I expected it to do that whilst I carry on working on something else.

I know you're finding this frustrating, but I don't think it's a bug.  AE's state is changing when the Render Queue finishes and just like any program, Windows then brings that up to the foreground.  The actual issue is your workflow of using Render Queue instead of Adobe Media Encoder.  Render Queue is the legacy method of exporting video.  Adobe moved all the latest compression methods to AME and continues to update them.  Render Queue also locks down After Effects, meaning you cannot continue to work in AE while it is rendering, whereas with AME, you can (although, it is worth noting that you send a copy of the comp to AME to render, so if you make changes, these won't be reflected until you send them again).

AME also doesn't have that alarming sheep bleep sound effect when a render fails.  The number of times I've jumped out my skin when that went off!

https://www.youtube.com/watch?v=mHONNcZbwDY

Hello? Is anybody there?

Could you provide a few more details? For example, when you say "after rendering finishes", I assume you mean you're rendering through AME, and AE pops to the foreground when AME is done, correct?