The “Vehicle” doctype is part of the ERPNext > Setup module, and I don’t want to modify the core files. Consequently, I attempted to add it to the Custom DocPerm. However, after each migration, the permission for it was consistently being removed.
I have successfully resolved the problem, and I would like to share the solution for the benefit of others encountering a similar issue.
The root cause of the problem was identified in some customizations of the vehicle doctype. It turns out that in a previously exported file, the new permissions were missing. During the migration process, Frappe checked this file for permissions and removed the missing ones, leading to the observed behavior.
I revisited the exported file, ensured that it included the necessary permissions for the vehicle doctype, and then re-ran the migration. This resolved the issue, and the custom DocPerms are now retained as expected.