Daddy You said on the other forum that shots of less than 50ml were very bitter? Are the 50ml shots less, or more bitter than the 20, or 30ml shots?
Are any of the shots sour?
Shorter shots will be more intense, but more prone to sourness. Longer shots will be more dilute, but more likely to be balanced (at a constant grind setting & dose).
Have you tried adjusting the grind to a coarser setting?
I was drinking some Lavazza Oro today, it’s not a coffee that I would describe as very bitter.