does anybody know what causes the geometry to disappear after a few frames with simulation nodes?

Weird. I'm surprised that this is working at all. I thought there would be no points to instance on after creating the first instance. The simulation zone isn't the culprit here though. The same happens here if i simply chain a few (7) instance on points nodes after another. I have to investigate this further. You can fix it by adding a realize instances node after the simulation. Be careful though. this gets ugly quickly :) And use radians if you pipe a vector into the rotation socket. -pi to pi should give you the 360° you are aiming for.

Ok, I got it. What you are doing is called nested instancing (instancing on an instance) https://docs.blender.org/manual/en/latest/modeling/geometry_nodes/instances.html#geometry-nodes-nested-instancing the page states:

Warning Only eight levels of nested instancing are supported for rendering and the viewport currently. Though deeper trees of instances can be made inside geometry nodes, they must be realized at the end of the node tree.