OK I sussed it out. It's not when I single click the buttons it's when I double click anywhere in the window.
Deselecting 'Double click a windows title bar' in Dock Preferences stops it from happenning.
....but it happens when I click anywhere in the window :/
Just tested this on a 2015 MBP with the Intel Iris Pro, 1536 MB GPU, running MacOS 10.14.5, it seems like that GPU has the same issues as the Intel HD 4000 with (Divide, Facet, Quantize, Trim).
This composition crashed a few times at first and then showed no output, I removed facetize and it worked as expected.