The canonical approach, which was developed for solving the sign problem, may suffer from a new type of sign problem. In the canonical approach, the grand partition function is written as a fugacity expansion: Z G (µ, T ) = n Z C (n, T )ξ n , where ξ = exp(µ/T ) is the fugacity, and Z C (n, T ) are given as averages over a Monte Carlo update, z n . We show that the complex phase of z n is proportional to n at each Monte Carlo step. Although z n take real positive values, the values of z n fluctuate rapidly when n is large, especially in the confinement phase, which gives a limit on n. We discuss possible remedies for this problem.