Question: Warning, expecting Range variable k blablabla... while trying to plot

I dont know what to do any further...

I have some function containing HeunG as a function

it is of the following form

f(k)=argument(functions containing HeunG) - ln(2)*k

now plotting this works...

But when differentiating with respect to k and then plotting it gives me the following message:

Warning, expecting only range variable k in expression (I*((1/2)^(1/2*I*k))^2*HeunG(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)*HeunGPrime(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)*ln(2)-((1/2)^(1/2*I*k))^2*((3/4*I-3/2*k)*D[2](HeunG)(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)+1/2*I*D[3](HeunG)(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)+1/2*I*D[4](HeunG)(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)+I*D[6](HeunG)(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2))*HeunGPrime(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)-((1/2)^(1/2*I*k))^2*HeunG(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)*((-3/2*I+k)*D[2](HeunGPrime)(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)+1/2*I*D[3](HeunGPrime)(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)+1/2*I*D[4](HeunGPrime)(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)+I*D[5](HeunGPrime)(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2))+I*((1/2)^(1/2*I*k))^2*HeunG(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)*HeunGPrime(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)*ln(2)-((1/2)^(1/2*I*k))^2*((-3/2*I+k)*D[2](HeunG)(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)+1/2*I*D[3](HeunG)(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)+1/2*I*D[4](HeunG)(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)+I*D[5](HeunG)(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2))*HeunGPrime(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)-((1/2)^(1/2*I*k))^2*HeunG(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)*((3/4*I-3/2*k)*D[2](HeunGPrime)(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)+1/2*I*D[3](HeunGPrime)(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)+1/2*I*D[4](HeunGPrime)(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)+I*D[6](HeunGPrime)(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)))*(-I/(-((1/2)^(1/2*I*k))^2*HeunG(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)*HeunGPrime(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)-((1/2)^(1/2*I*k))^2*HeunG(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)*HeunGPrime(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2))+I*abs(1,-((1/2)^(1/2*I*k))^2*HeunG(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)*HeunGPrime(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)-((1/2)^(1/2*I*k))^2*HeunG(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)*HeunGPrime(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2))/abs(((1/2)^(1/2*I*k))^2*HeunG(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)*HeunGPrime(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)+((1/2)^(1/2*I*k))^2*HeunG(-2,5-3/2*I*k+1/2*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1+I*k,1/2,1/2)*HeunGPrime(3,-9/2+3/4*I*k-3/4*k^2,-1+1/2*I*k,-1/2+1/2*I*k,1/2,1+I*k,1/2)))-ln(2) to be plotted but found names [D[2](HeunG), D[2](HeunGPrime), D[3](HeunG), D[3](HeunGPrime), D[4](HeunG), D[4](HeunGPrime), D[5](HeunG), D[5](HeunGPrime), D[6](HeunG), D[6](HeunGPrime)]

D[i] are the Differential Operators acting on the arguments of HeunG since it is evaluated at some fixed point in this case t=1/2

But why does the plotter seem to understand them as variables?