[branch] if()
{
}
Inside a custom node, this works as expected. Anything under IF cannot contain gradient functions, so SampleLevel or SampleGrad must be used, and derivatives must be calculated before the branch in case with SampleGrad.
Also, if you modify output of custom node by anything, that depends on sampling another texture, branching fails. I do not see apparent cause for this.
There is still no ticket for the whole issue btw.