The filters that come with Intex pools are not that reliable to begin with, and the cartridge is sub-par as well. You probably just have a dirty filter when vacuuming, so try cleaning it out before you vacuum, until you get a "real" pump. I think your pump might be oversized as well, and I think Intex realized this, as the new ones are around 1500-2000 GPH.
HTH
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