Thank you for you helpful advice! Here are my settings:
# Stepper module pins ( ports, and pin numbers, appending "!" to the number will invert a pin )
alpha_step_pin 2.0 # Pin for alpha stepper step signal
alpha_dir_pin 0.5 # Pin for alpha stepper direction
alpha_en_pin 0.4 # Pin for alpha enable pin
alpha_current 0.4 # X stepper motor current
alpha_max_rate 24000.0 # mm/min
alpha_acceleration 2500 # mm/sec²
beta_step_pin 2.1 # Pin for beta stepper step signal
beta_dir_pin 0.11 # Pin for beta stepper direction
beta_en_pin 0.10 # Pin for beta enable
beta_current 0.6 # Y stepper motor current
beta_max_rate 24000.0 # mm/min
beta_acceleration 2500 # mm/sec²
I will increase alpha_current to 0.5 and retry.
I would have never known about these settings had you not mentioned them.
Thank you.