Coppersmith's method implementation
Coppersmith's method, parameterized by $\epsilon$, finds all roots $\le \frac{1}{2} n^{\beta^2/\delta - \epsilon}$ to a polynomial $f(x)$ of degree $\delta$ modulo an unknown factor of $n$ of size $\ge n^\beta$. In your case, $\beta = 1$ and $\delta = \{4,5,6,7\}$. 

Sage defaults $\epsilon = \beta/8$, which in your case would be $0.125$. However, $55555^{1^2/\{4,5,6,7\} - 0.125}$ is, respectively, $\{1.96, 1.13, 0.79, 0.61\}$. Only the first (almost) respects the bound. But if you tweak small_roots with an appropriate $\epsilon$, e.g., f.small_roots(epsilon=0.02), you should get more satisfactory answers.