I suspect the error is in the iterative solver; I don’t think changing anything in stepcompress will change anything.
I can reproduce this locally in batch mode: python ../../klippy/klippy.py -i test.gcode -o output -d dict/samd51p20.dict test.cfg
With a test.gcode of:
M83
G1 E-120 F60
M83
G1 E120 F600
M83
G1 E-120 F600
M83
G1 E120 F60
M83
G1 E-120 F0.6
It is the last line of the test.gcode that results in the error.
-Kevin