Still working on this, however slowly:
Like @allevato mentioned:
but we still see some of these details leaking through and I even had a weird edge case with a class' v-table being invisible to a descendant class and not clearly related to implementationOnly imports anyway. The problem was not minimally-reproducible but the fix was adding final to some private methods of the base class. As v-table layout (in fragile builds, resilient is at runtime) happens before devirturalization this was an acceptable fix at the time but we weren't able to diagnose the problem further. If anyone else is working on this actively, please reach out.