These past few days I've been checking on the current Arbitration node quite a few times, mostly between Wolf runs, sometimes while doing other stuff, and sometimes on Semlar's website.
I wanted to test something, but haven't seen a single Excavation.
I've seen Defence missions most of the time, then some Survivals, the occasional Interception. Does anyone know about the chances with which these occur? It does not look like they have equal frequency -- or am I just that unlucky?