Jett 130 and Zero and sit bone LUMP

[KnottedYet]

Knot - out of curiosity, how "major" would the avulsion issues/symptoms be?

Well, there'd be some bleeding. (are you still on anticoagulants?) The muscle would be inhibited. (which would lead to more imbalances and more irritations and more compensations) Depending on the size of the avulsion the chip itself might be sawing on soft tissue, causing your body to be inflamed there, and oh.... making a big lump. You'd also be in a lot of pain and probably unable to sit without more pain.

Definitely time to pay a friendly visit to the doc.

Once the problem is isolated the next step is figuring what the cause was in the first place. Without a trauma (did you crash? is it the older saddle?) to the ish tub, the likely root cause is an imbalance of forces acting on the ish tub.