X_DOC_MIGRATION_SECTION_MISSING
Means
a released major has a summary row in wiki/Upgrading.md and no → X.Y.Z, entry by entry section for it to point at
Typical cause
the row is a promise and the section is the thing promised. X_DOC_MIGRATION_COUNT_STALE verifies the row's text and never that the section exists — which is how 1.x → 2.0.0 pointed at nothing through six releases, for the largest major this project has shipped
Fix
write the walkthrough in wiki/Upgrading.md under a heading of the form ## 1.x → 2.0.0, entry by entry naming the version the cause names, one subsection per entry of that section of CHANGELOG.md