There are a lot of unknowns in this situation you’ve described.
Astringency is akin to chewing on grape skins—mouthpuckering. The term is easily mistaken or misused to mean bitter, harsh-flavored, or something off-flavored. The astringency is supposedly due to tannins.
With all respect to Jeff Foxworthy, here are some suggestions:
Water—if your water has a high residual alkalinity or sulfate level, your beer may seem astringent.
Water—if your chloride to sulfate level is low, your beer may seem astringent, or bitter.
Mash—if you’re over sparging with hot water (>170 F), then your beer may be astringent (due to tannins).
Mash—if you’re allowing the mash pH to rise higher than 6.0, then your beer may be astringent.
Hops—if you’re using hops according to schedule, but not chilling your wort quickly after knockout (turning off the heat) with the immersion chiller, then your beer may be astringent due to increased hop utilization.
Refractometer—if you’re using a refractometer with ATC—I’d go with that. Hydro readings should be done at 60 F. Are you cooling the wort down before checking the reading. Learn the refractometer method (it just requires a few drops and it’s fast!).