One return jet not working

[oguzal]

One of the return jets stopped worked, i did a backwash and after that it worked for 2-3 secs
The valve to control the return jets are set correctly
The pressure gauge on the filter looks good (20)
What I should check?

 

[AQUA~HOLICS]

RETURN JET/ in the spa or in the pool?

 

[oguzal]

Pool