Power steering issue

VIN #1GDJG31K991106080.
This is a customer's cube/box van; this customer is in Georgia, I'm located in South Carolina. He acquired it from another company location in June 2018 and started having power steering issues with it in July. He was at a customer's location delivering uniforms when it started having problems and the customer did something to it to get it back to the location but they don't know what was done. It worked a short period of time but then the power steering would only work with the RPM's up and the vehicle moving; sitting still it took two hands to turn the wheel and the pump was making noise. In January this year they authorized me to repair it; I installed a NAPA
re-manufactured pump on it and bled the system but the pump continued to make noise and four weeks later it started leaking. I installed a new OEM pump and bled the system with no problems and then in March the pump seized, breaking the serpentine belt and emptying the system fluid. I disconnected all system components from each other and used shop air to flush all components free of fluid then replaced all system hoses, pump, belt and cooler lines with OEM parts; bled system but continued to have pump noise so told customer to not drive. I went back the next week to diagnose and found it had been driven over 200 miles; the pressure line from the hydroboost to the gearbox had separated from the crimp, the pump was seized and the system fluid was empty. I replaced the pump and line, filled the system then spent the next hour with the front end on jack stands and had a helper follow the procedure I've attached to bleed the system of air. Once I was certain it was free I started it and let it run for ten seconds then shut down and performed the bleed procedure again; I repeated this three times and the system was free of air. I took it off the stands, started and moved the wheels side to side while watching the fluid for aeration okay, so brought fluid to the proper level and test-drove. Less than a half mile later after turning on to a straight highway and without turning the wheels I heard a pop so pulled over, shut off and raised the hood and found the same OEM hose from before had separated from the crimp going on the steel fitting going to the booster. I brought it back and found the pump wasn't seized but the system was empty of fluid and haven't done anything further. I've been a vehicle tech for forty five years and have replaced a lot of power steering pumps and am completely mystified about this issue and need help.