I think that it was Brian Edmonds that first brought this issue up. The new suspension puts more pressure on the bottom support structure because the thin wall of the red threaded cylinder has a much smaller cross sectional area vs. the old springs. Brian found that his bottom spring supports were deforming. He fixed this by installing a big washer, 2" ID, 4.5" OD between the read threaded cylinder and the spring base structure that is integral with the trailing arm.
I’m pretty sure those dimensions are right. The conversation with Brian was a couple years ago. I bought what Brian recommended, I’ve not installed them tho.