The top section of that is the ATS, its a generac style contactor similar to asco and kohler etc. just with generac control logic, no way for that to back feed when properly hooked up, ive never ever seen that happen.
I have seen this problem several times with leaks in unions on the suction side of the pumps. The issue only came out when psi rose and would never leak externally, only let the pump **** air in the suction side, it would also come and go with temperature and other factors. Are you sure there is...
I have used them in several off grid sites, i do alot of off grid contracting and where i live has tons of islands and cays, they do work surprisingly well ive gone from no signal to steady 80Mbps of 4glte data
i bought a similar warehouse deal on amazon for an rmw castors trolly, it had major damage to the point where it affected functionality and it also was missing the axle, i fixed both issues and kept it but mine didn't even say major damage it said minor cosmetic.