Nice @keesscherer ?
I notice there are some hot pixels still showing, these could easily be removed (and most efficiently) with an adequate Bad Pixel Map.
The Bad Pixel Map will never degrade image quality (can’t inject noise) and will remove the non-linear pixels from your light frames.
Unlike outlier rejection filters, it can’t hurt your SNR ? so it’s a much better solution to get rid of those hot pixels.
Outlier rejection should always be considered a last resort to remove artefacts in your data ?
Some more good news, I have been profiling APP on my MacBook and after having made 2 big stacks in a row the application became really slow, like you describe.. so I am now looking in detail for possible memory leaks and inefficient programming. I think I have already found a couple of problems which I’ll try to fix.