When developing econplayground, some of the functionality requires two functions on a graph: one linear, one non-linear. For the linear function, I can get away with just using a JSXGraph Line, and for the non-linear curve, a Functiongraph.
Line A is a JSXGraph Line and Line B is a Functiongraph:
In this example, the intersection point disappears when dragging the orange line, or when dragging the blue line to the left.
One workaround is to use a Functiongraph for both lines, suggested by a user on StackOverflow.
Here, both lines are Functiongraphs: