Can anyone give me tips on how to proceed with this triac/optocoupler/motor circuit fix?
I think you need to increase the igt of triac reducing R2 from 1K to 220 or 100 ohms, in addition optocouplers with inductive loads requires more input current to work properly; if you have the oportunity to change optocoupler I recommend to use the best optocoupler IL420.