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
super(Many2many, self)._setup_regular_full(model)
        if self.relation:
            m2m = model.pool._m2m
            
            invf = m2m.get((self.relation, self.column2, self.column1))
            if invf:
                comodel = model.env[self.comodel_name]
                model._field_inverses.add(self, invf)
                comodel._field_inverses.add(invf, self)
            else:
                
                m2m[(self.relation, self.column1, self.column2)] = self
    def check_schema(self, model):