"you are comparing oranges to opossums " LOL, now there's a great analogy
Probiotics (VSL DS3 specifically) did absolutely nothing but give me crazy gas, and I had no improvements within my UC symptoms from them. So much so, that my dear wife was calling me fartzilla, and repeatedly threatening to force me to sleep in our guest bedroom. I gave it a fair shake, assessed, and kicked probiotics to the curb. Not everybody has an improvement with probiotics, but some certainly do. Everything that's UC is truly hit-or-miss with wildly different responses from different people.
I don't buy into the "die off" bit. You're flooding your digestive system with millions or billions of microorganisms and they are going to party down there and do their probiotic thing (hopefully doing more help than harm). There's so many all at once that they can cause bloating, gas, and general discomfort. You could try taking less, as perhaps you're ODing.