ABS Issue

So, I am having an issue with our 2008 Toyota Prius (220k miles) that seems to be related to the ABS system (???).

Symptoms are:
1) When pressing the brake to start the car, the pedal loses resistance temporarily and then "pushes back" to the original resting position. Brakes work normally other than that.
2) Brake, (!), ABS light on
3) Check engine light also on, but this popped up recently (week ago) and have had the other lights on for a few weeks now. Only code that reads on an OBD II scanner is P0102.
4) "whirring" Sound from ABS actuator can be heard while car is on (whether brake is being applied or not) every 5-10 seconds.

Here is what I have tried so far:
0) Checked ABS fuses
Result: All good.
1) Cleaned the Mass Air Flow Sensor
Result: Lol nothing.
2) Replaced the front rotors, pads and wheel speed sensors
Result: Weird braking issue at start up resolved for ~24 hours before returning. Reset the ABS light and lights stayed off for about 24 hours as well.
3) Replaced the ABS actuator (Used with 60 day warranty)
Result: Sore back, cursing and almost calling a tow truck after improperly plugging in the hybrid battery unit. Lights disappeared spontaneously and stayed off for about three days. Weird braking symptoms also resolved, but returned after about 5 days. Repetitive, ABS actuator noise could he heard exactly like before replacement, immediately after replacement.

I am in the process of picking up a cheap laptop and Mini-VCI cord to run Techstream hoping this will illuminate the root cause.

What do you guys think? I know if it is the ABS actuator, the one I bought could also be dysfunctional. What is really confusing me is that the issue was resolved after replacing the ABS actuator for a few days before returning.

I'm assuming the check engine light is unrelated? I've ordered a mass air flow unit hoping this will resolve the check engine light.

Thanks in advance!