Pump losing prime

[steveb21]

Losing prime all of a sudden....

I have:
Tried ports (Skimmer, Sump and Vacuum) one by one.
It eventually does get started after a few mins... however when i switch it off all the water comes rushing back and empties out the pump basket.
When primed my gauge is hardly showing any reading (about 1/10 of what it would usually be). The gauge low reading has coincided with the prime issue.

I take it I have a suction leak?
Any tips to resolve please?

 

[Pool_Medic]

If it eventually fully primes then it’s a pressure side leak that allows the rushing air in and breaks the circle of water.