I feel like you guys are dragging me around in circles.
Don't blame me. I just got here.
If you create a specific water profile for each batch then you should have known that it was bad advice to use that much gypsum and dismissed it. But if you're willing to follow advice which you knew was bad to begin with, why haven't you
bottled a batch yet to rule out the keg as the problem?
The problem is you haven't been troubleshooting this very well at all. You have not approached this logically. I know you will take offense to that, but sometimes truth hurts. The fact you haven't bottled anything demonstrates this.
This is how you should have done it:
1. Brew a basic batch with distilled water. Water that you buy in a store that comes in a plastic jug. Not water from a Glacier vending machine.
2. Use your standard profile you just mentioned. In fact, before you brew, post your grain bill, strike water and sparge water amounts, and the additions in grams that you plan to make to each so everyone can agree they are correct. (When you make the additions to the water, and they are all dissolved, perhaps you can take a sample and send to Ward labs for analysis.)
3. After you boil, split the wort into TWO SEPARATE BATCHES. Cool each as normal. Use new yeast in one batch, and use your yeast in the other. Label which is which.
4. After fermentation, you will have two batches. Keg some of each batch separately like you normally do but also BOTTLE a bunch of each batch separately.
You now have essentially 4 separate batches:
1. Old yeast, bottled
2. Old yeast, kegged
3. New yeast, bottled
4. New yeast, kegged
This would help you eliminate potential causes, depending which have off-flavors and which do not. In one batch you will be able to isolate whether it was a yeast issue, a fermentation issue, or a kegging issue. Or, more importantly, none of them!
If they all have off flavors, then it is not the yeast, and it is not your keg. If your analysis from Ward Labs comes back with the right levels of everything that you predicted when building your water profile, you can safely rule that out.
There you go. ONE brew day would eliminate almost every concern you have and point you to whatever might be the actual culprit.
THAT'S how to troubleshoot it. If you do not do it this way, no one will be able to help you.