Filter not working but Polaris is

[Stingray454]

I have a backyard inground pool with a hot tub which flows into the pool when the filter is on. when the filter is on and pumping the water is returned to the spa which then overflows into the pool, at the same time I have a Polaris vacuum which goes at the same time. I just walked into the backyard and noticed that the Polaris is working however the water level of the spa is low and water does not appear to be being pumped into the spa. when I inspected the filter pump the motor was not too hot to hold my hand on but it was quite hot, it was vibrating but and I could see water bubbling under the cover but it didn't seem to be going at full speed. Does anyone know what is going on? Any help would me much appreciated.

Jeff