The ultimaker ptfe spacer warped -- this happens periodically (too periodically) under normal use.
I put a new spacer on the warden order list, but I’m also going to try making a substitute part on the lathe that would be lined with with plain old ptfe tube (cheap and plentiful), and thread into the UM2 heatblock and nozzle.
Will keep folks apprised. Until then, expect ultimaker to underextrude horribly, especially after the 1st layer.