Same, I was never able to debug why dropout > 5% really hurt convergence speed for my toy LLMs. I chalked it up to the models not having enough parameters to fit fineweb and just stop using it.
My intuition is very undeveloped on this, but it makes some kind of sense to me that dropout would make convergence slower, because you're ignoring a bunch of parameters in every batch. The goal seems to be to get a better, more general model by trading off some training time.