Also having some unhappy adventures with the new bedding. Long story short, I was told the mix would contain a portion of sand, but when delivered I learned that it contained "topsoil" instead of sand, which in this country means "clay". The weather was cold, the clay was wet, and evidently some unfriendly opportunistic bacteria may have affected the stems of my plants as well. I suspect "blackleg" as known from potato - because there was blackleg in several bags of potatoes I brought home from the store
and also on carrots (which looked perfect for three days at least).
So my transplants developed symptoms of "tomato pith necrosis" - as far as I can tell - I haven't cut any but they had yellowing new growth and then developed swellings on the stems. I did a soil intervention to break up the compacted mess and introduce some friendlier microbes, and the weather warmed up and they seem to have "outgrown" the condition, for now.
For your interest, pics of stem swellings. Some plants dropped fruit or flowers, some are setting normally in spite of the vascular stress.