Load the finite element package:

In this example, a Péclet number has been computed that indicates that the differential equation may exhibit instabilities. The Péclet number is only computed if an explicit mesh is given:

The solution is to use a finer mesh:

In this case, the time-dependent PDE is treated as a three-dimensional spatial PDE because an initial condition is missing. The three-dimensional PDE is convection dominated:

If the intent is to compute a time-dependent differential equation as a pure spatial solution, then the issue indicated by the message can be avoided by making use of a finer mesh:

If the intent is to compute the time-dependent differential equation as a time-dependent equation with a spatial discretization, then the initial condition and the time domain should be separated from the spatial domain: