I've had beer go from grain to glass in 2 weeks! There are many differences to consider in your situation. The recipe for one, the water (as you've pointed out), ingredient quality/age, fermentation temps etc.
The high bitterness you've described could be because of a high % of sulphate in...
Also good to remember that starsan is a no-rinse sanitiser. If you rinse it away then you're defeating the purpose of having used it in the first place. I highly doubt that's what your problem is, but just putting it out there none the less.
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