  Feynman integrals can be expanded asymptotically with respect to some small
parameters at the integrand level, a technique known as the expansion by
regions. A naive expansion by regions may break down due to divergences not
regulated by the spacetime dimension, exemplified by the rapidity divergences.
A criterion to identify unregulated divergences is provided in this article.
The analysis is conducted using both parametric and Mellin-Barnes
representations, leading to a consistent conclusion. Based on this analysis, it
is proven that the presence of unregulated divergences implies the degeneracies
of regions, which may help to explain phenomena like the collinear anomaly.
