1. `copy_cache` in `models.py` recursively copies the caches to environment, 
2. which in
```python
def _compute_related(self, records):
        """ Compute the related field ``self`` on ``records``. """
        others = records.sudo() if self.related_sudo else records
        if records.env != others.env:
            copy_cache(records - records.filtered('id'), others.env)
        values = list(others)
        for name in self.related[:-1]:
            values = [first(value[name]) for value in values]
        for record, value in zip(records, values):
            record[self.name] = value[self.related_field.name]
```
3. copies failing cache values that have been produce previously by this line:

`models.py : def _prefetch_field()`
```python

        try:
            # THIS ONE
            result = records.read([f.name for f in fs], load='_classic_write')
        except AccessError:
            # not all records may be accessible, try with only current record
            result = self.read([f.name for f in fs], load='_classic_write')
```
I checked it's exactly the same `FailedValue` object, which is later accessed without intent (not refreshed) by the fact that the buggy environment is copied to sudo (and not refreshed).


""" The value of such a field is a recordset of size 0 (no
    record) or 1 (a single record).
    :param comodel_name: name of the target model (string)
    :param domain: an optional domain to set on candidate values on the
        client side (domain or string)
    :param context: an optional context to use on the client side when
        handling that field (dictionary)
    :param ondelete: what to do when the referred record is deleted;
        possible values are: ``'set null'``, ``'restrict'``, ``'cascade'``
    :param auto_join: whether JOINs are generated upon search through that
        field (boolean, by default ``False``)
    :param delegate: set it to ``True`` to make fields of the target model
        accessible from the current model (corresponds to ``_inherits``)
    The attribute ``comodel_name`` is mandatory except in the case of related
    fields or field extensions.
    """
    type = 'many2one'
    column_type = ('int4', 'int4')
    _slots = {
        'ondelete': 'set null',         
        'auto_join': False,             
        'delegate': False,              
    }
    def __init__(self, comodel_name=Default, string=Default, **kwargs):
        super(Many2one, self).__init__(comodel_name=comodel_name, string=string, **kwargs)
    def _setup_attrs(self, model, name):