Consider the following piece-wise function.
ClearAll["Global`*"];
$Assumptions = {L > 0};
f[x_] := Piecewise[{{Subscript[A, 0] + Subscript[A, 1] x, 0 <= x < L/2},
{Subscript[B, 0] + Subscript[B, 1] x, L/2 < x <= L}}];
f[L/4]
The output which I get is the strange result
However, when I replace L with a numerical value then I get a correct output. What is going on here?