Pool pump aeration
Air in the pump is very easy to spot. As the water flows out, you can hear the "characteristic" shooting of air bubbles and, in extreme cases, it stops flowing altogether. The cause is obvious. The pump is sucking in air. It is worth checking the installation for leaks; this is usually where the problem lies.
Check that the water level is right. When you use the pool, you cause it to move in the tank. When the water level is at its limit, rapid rippling of the water, e.g. by jumping children playing, can cause the suction nozzles to be partially above the waterline.
It can also happen that some component in the pump is leaking. Seals can lose their properties when exposed to excessive heat. If the previous causes are not detected, it is worth having the pump serviced.