@liffo said in Smart effector with very odd behaviour:

M558 P5

I believe the correct probe type is P8

https://duet3d.dozuki.com/Wiki/Smart_effector_and_carriage_adapters_for_delta_printer#Section_Commissioning

6 and 7 flashes would indicate the strain gauge is out of tolerance. Have you tested when the smart effector is not mounted? Perhaps it's been over tightened?