Hello and welcome to just answer. Let me see if I can help you with this. This can be caused by a failing master cylinder, or the ABS valve assembly itself. I see more master cylinders cause this symptom. If you are sure that the brake system was bled properly, Then replace the master cylinder and re bleed the system. If the problem persists, then go ahead and replace the ABS valve and again, re bleed the system.
I hope this information helps, and let me know if you need further assistance with this.