Thank you @kfrajer, there’s some great info there.
It turns out I’m an idiot and the problem was an incorrect loadShape() path. It made processing-java hang, and after about 3 or 4 minutes, chew up 100% of the server CPU.
In the process I switched over to using exported linux executables, as you suggested, instead of sketches running via processing-java. These still failed but didn’t bring the server down with them.
All solved now, and executables seem more stable.
Cheers
Dan