Above Ground Pool Vacuum PSI drops from 12 PSI to 3 PSI and isn't picking up anything surrounded by pool. Please recommend. I have a 24' round above ground pool. This is...

I have a 24' round above ground pool.
This is 5th summer.
Pump and filter are fresh and on 2nd season.
Winterized everything well.
New hoses and immobilize connections with no leak.
Took apart and put new sand surrounded by filter last summer.
Tried 2 different vacuum hoses - same problem.
Do I entail new vacuum come first? Any recommendations?
I read a vacuum organizer with wheel is better than standard one with brushes.
Don't know why I'm losing so much pressure.
Never have this problem before.
No blockages within hoses.
Already backwashed.
Chlorinator is set to FULL.
I primed the pump.
The rubber seal is immobilize in the lid of pump.
No petcock.
Pressure is upright (12 psi) when pump is running normally or contained by Rinse cycle.
Please help!
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