calculation and analysis: possible error related to the BesselI derivative

In Mathematica 12.0, I execute the following code:

f(x_) = BesselI(0, x);

that comes back BesselI(1, x) as expected. But if I enter

f(x_) = BesselI(0, 1.0 x);

I get

0.5 (BesselI(1, 1. x) + BesselI(1, 1. System`Private`DerivativeX(1.)))

Further, D(f(x),x) Returns the expected result. I tried to exit the kernel without changes. Is this a mistake or something is wrong with my installation?