In a multi-tenant case, all the tenants share one single codebase (for example, DocType versions defined in apps like erpnext and frappe).
But likewise in a multi-tenant case, each tenant’s data set restore must be migrated and patches applied to their data set. So patches may possibly raise an error that requires another (earlier?) DocType version, so the case for reload-doc may occur, or to add or change a patch.
That said YMMV - what you observe may differ from my own tentative theory, as I have no practical experience with multi-tenant migration…
This post may help with your understanding Need a better understanding of MultiTenant configurations