Strawberry-rhubarb pie: the filling sets as it cools

Useful to know

King Arthur Baking's Strawberry-Rhubarb Pie combines fruit and thickener inside a double crust. The recipe notes that the filling sets as it cools. [1]

Cutting a hot pie is not equivalent to testing a cooled one. Before increasing thickener, check slicing time and thickener type; the listed alternatives do not all use equal quantities.