Performance different in R vs. Python!

I’m experiencing different results in R and Python when I’m making a really basic model on the iris data set.
94% vs. 0.97% holdout accuracy, but for a more complex project I’m getting almost 15 percentage points difference!

For the test on the iris data set, the default parameters are the same and I’m using the same seeds.
I know the RNG is different between the languages, but is this really the reason or are there other reasons causing these differences?

Yes, R uses its own RNG.