A small, detailed, print to test ability of printer to retract (not print) between towers of varying widths and matching gaps, as well as to print a thin layer that does span the tops of all the towers in X & Y.

I discovered that my printer (Portabee) stopped printing when Cura had 'retract' enabled! (This print is with retract disabled.)

Filament feed/retract was observed to be random amounts (both feed distance and retract distance!) with retract enabled. Feed stepper needs to be investigated / repaired.

Follow up: retraction speed slowed, retraction distance reduced, grip on extruder loosened (avoid shredding)... retract now works!