Ihave a high pressure well which does not require a foot valve and there is only a single feed line from the well. The pump is a grundfos with a bladder tank.
The system loses pressure rapidly after the pump shuts off. What could be the cause ot this pressure loss wthin a very short period. There are no vidsible water leaks in the system.

Sounds like you have a leaking checkvalve. The pump pumps up to pressure and shuts off, but the leaking valve allows the water to simply flow back into the well. When the pump cuts off, watch your pressure gauge. If you see pressure consistently falling, then you know your problem. See the link below to see what the checkvalve will look like.

Water system check valve location & purpose - private pump and well system do-it-yourself repairs