End mills brake seemingly random

Hi,
I had my Stepcraft D2 840 for some years and it works like a charm on wood.
I recently started a project (flash drive enclosure/heatsink) which requires the use of aluminium.
I have now broken 3 end mills in a row and still have absolutely no idea why, it doesn't vibrate, the surface finish isn't good but perfect, still the end mill just breaks every time with zero indication.
In the first picture you can see where it broke(top right corner) and that it didn't brake at a corner at this exact depth before, so why did it brake this time? After that are my feeds and speeds.
I also have a video of it but I can't upload it because it is 35 times the file size limit.

What should I do differently?