Can the Reset generator be another source of problems because it is generating false reset pulses from the noise from the motor?
Absolutely if not properly decoupled

In addition there is a large difference between noise sensitivity from brand to brand of 'equivalents' (all are called 1232). In a board I inherited where the traces to the decoupling of the supervisor are more than 1" long (argh!) all brands work satisfactory when an additional capacitor is soldered straight between the Vcc and ground pin of the 1232. But if that capacitot is not added, boards with the Maxim 1232 work fine, but some boards with Microchip 1232 fail.

Erik