Although accessibility guidelines and automated checks are widely available, mobile applications continue to present barriers that exclude users with disabilities. Prior work has emphasized guideline conformance and static analysis, but little is known about how accessibility problems actually arise during the development process. This work analyzes real accessibility issues reported by developers in open-source mobile projects. A manual review of 256 GitHub issues related to accessibility (in Kotlin native Android applications), combined with thematic analysis, yields an empirically grounded taxonomy of problems not deeply considered before. The taxonomy captures recurring issues in assistive technology support, visual accessibility, and touch and gesture interaction. Our findings indicate that many accessibility issues are not due to the absence of elements, but rather to incorrect or missing semantics that impede assistive technologies. These findings provide a basis for improving accessibility rules used by existing static and dynamic analysis tools, as well as developer practices and future research efforts.