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
ids = OrderedSet(command[2])
                elif isinstance(command, dict):
                    ids.add(comodel.new(command).id)
                else:
                    ids.add(command)
            
            return process(tuple(ids))
        elif not value:
            return ()
        raise ValueError("Wrong value for %s: %s" % (self, value))
    def convert_to_record(self, value, record):
        return record.env[self.comodel_name]._browse(value, record.env, record._prefetch)
    def convert_to_read(self, value, record, use_name_get=True):
        return value.ids
    def convert_to_write(self, value, record):
        
        result = [(6, 0, [])]
        for record in value:
            if not record.id:
                values = {name: record[name] for name in record._cache}
                values = record._convert_to_write(values)
                result.append((0, 0, values))
            elif record._is_dirty():
                values = {name: record[name] for name in record._get_dirty()}
                values = record._convert_to_write(values)
                result.append((1, record.id, values))
            else:
                result[0][2].append(record.id)
        return result
    def convert_to_onchange(self, value, record, fnames=()):