I’ve had similar problems. The process that works 99% of the time for me:
(1) Heat to extrusion temp,
(2) Slowly extrude a small amount (~5mm), then immediately
(3) Slowly and steadily retract, continuously, pulling upward slightly on the filament so that when it clears the hob it pulls out of the idler assembly. If it stops moving upward at any time during #3, reverse direction until a little extrudes from the nozzle, then try #3 again.
This process does result in a “long thin string” as you observed, but that hasn’t been a problem for me – the string just pulls out, and if any is left in the filament path, it hasn’t cause any problems feeding new filament.
I found out REAL FAST not to try a “cold pull” with Aerostruder. I managed to wedge some A910 in the guide tube (the tube between the hob and the heat break) so tight that I had to completely disassemble the extruder and remove the guide tube to clear it.