Anyone know what the spring and bypass valve in the oil pump assembly do? What would be the symptoms of a sticky piston in that valve not moving easy or getting stuck?

 

I believe they act as a relief valve. When the pressure gets too high, it opens up and drops the pressure. If the piston gets stuck in the relief/bypass mode, then there is little to no pressure in the system. By shimming the spring, the assembly has more pressure because the spring is compressed due to the shims) so it helps the piston return to the closed state.