The solution is to set default dimensions (function GESCDE), for codes MF* and MK* for all mandatory dimensions.
If the dimensions are set as mandatory on the company, they must be populated in all the production tracking documents. Even if the fields are hidden or just displayed in the production tracking transactions.
This is because when dimensions are mandatory, they must be populated on the GL Journal Entries which will be created from the manufacturing trackings.
The journal entries are created from STOJOU or from WIPCOST (depending on your setup), by FUNSTKACC or FUNWIPACC. The dimensions in STOJOU and WIPCOST comes from the production trackings (release products, materials, operations), so this is the reason why they must be populated there.
In regard to the situation where the accounts used for manufacturing do not require dimensions, although it is not mandatory to manage the dimensions on the accounts, in manufacturing we don't know which accounts will be applied. The accounts are known too late : i.e. when the GL journal entry is created. This means the dimensions must be mandatory in the production tracking documents even if the GL journal entry will not manage those dimensions because of the account's setup.