Tonight was more of the same but now it consistently did this during calibration:
-- RA forward and reverse - OK
-- DEC forward - OK
-- DEC reverse - goes for just one step and claims that the calibration is successful.
Guiding goes nowhere after this.
I again, booted/rebooted, connected/reconnected cables and finally it worked.

Can a flaky cable or a loose USB connector cause this?
If it's a cable/connector - why it only affects the DEC?