Follow up - My flavor has improved dramatically. Here's what I changed:
1. Started fermenting in stainless corny kegs and only use "closed" CO2 pressure transfers to move wort from primary fermenter to serving keg.
2. Got the Brew Bag, which has very fine mesh and does not allow for grain particulate to build up in the seams.
3. Don't bother using my PH meter, even though I just bought a brand new one - and just add recommended dosage of 10% phosphoric acid based on Brewfather/Beersmith.
4. Use my tap water, but with campden tablets to eliminate chlorine/chloromine.
5. Allow ample time for yeast to complete fermentation. Cold crash and give time for flavors to mature. I use kveik yeast now, so my impatience is mitigated by a faster ferment with kveik.
6. Only gently squeeze the bag, and do not wring out every last ounce of wort. Rather, I just rinse it with some 170 F water.
7. Thoroughly sanitize as always.
I believe the significant improvement in my flavor came by fermenting with very minimal oxygen in the stainless corny keg. That bitter off-flavor still might be slightly present, but I cannot detect it nearly as much as my previous batches. Something must have been getting contaminated from transferring with an auto-siphon or getting oxidized. Either way, both siphoning and transferring are done with CO2 now, so the beers are tasting mighty fresh!