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).


odoo/fields.py
if not validate:
            return value or False
        if value in self.get_values(record.env):
            return value
        elif not value:
            return False
        raise ValueError("Wrong value for %s: %r" % (self, value))
    def convert_to_export(self, value, record):
        if not isinstance(self.selection, list):
            
            return value if value else ''
        for item in self._description_selection(record.env):
            if item[0] == value:
                return item[1]
        return False
    def convert_to_column(self, value, record):
        """ Convert ``value`` from the ``write`` format to the SQL format. """
        if value is None or value is False:
            return None
        if isinstance(value, unicode):
            return value.encode('utf8')
        return str(value)
class Reference(Selection):
    type = 'reference'
    @property
    def column_type(self):
        return ('varchar', pg_varchar())
    def convert_to_cache(self, value, record, validate=True):
        
        def process(res_model, res_id):