Yes, these are the power amplifiers, driver and current feedback peripherals of the motors.
In cases where the power amplifiers, drivers, current sensors have gone faulty, usually you receive different error codes.
But it's conceivable if what you are referring to as 'blocking' meaning the motor appears to be 'jumping/cogging' round instead of smooth rotation that any of those components could have developed a fault and the 'encoder is the first error it see's in the failure process'.
Take care when dealing with the power blocks, as they contain high voltages, so always power off the controller and take some PN circuit measurements to confirm the PN levels have reduced near 0V before disconnection and removal, otherwise you may cause damage or injury.