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).


return ','.join(name for id, name in value.name_get()) if value else ''
    def convert_to_display_name(self, value, record):
        raise NotImplementedError()
    def _compute_related(self, records):
        """ Compute the related field ``self`` on ``records``. """
        super(_RelationalMulti, self)._compute_related(records)
        if self.related_sudo:
            
            target = records.mapped(self.name)
            target_ids = set(target.search([('id', 'in', target.ids)]).ids)
            accessible = lambda target: target.id in target_ids
            
            for record in records:
                record[self.name] = record[self.name].filtered(accessible)
    def _setup_regular_base(self, model):
        super(_RelationalMulti, self)._setup_regular_base(model)
        if isinstance(self.domain, list):
            self.depends += tuple(
                self.name + '.' + arg[0]
                for arg in self.domain
                if isinstance(arg, (tuple, list)) and isinstance(arg[0], basestring)
            )
class One2many(_RelationalMulti):