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).


""" Placeholder for a value update; when this value is taken from the cache,
        it returns ``record[field.name] | value`` and stores it in the cache.
    """
    def __init__(self, field, record, value):
        self.args = (field, record, value)
    def get(self):
        field, record, value = self.args
        
        del record._cache[field]
        
        value = field.convert_to_cache(record[field.name] | value, record, validate=False)
        record._cache[field] = value
        return value
class _RelationalMulti(_Relational):
    """ Abstract class for relational fields *2many. """
    def _update(self, records, value):
        """ Update the cached value of ``self`` for ``records`` with ``value``. """
        for record in records:
            if self in record._cache:
                val = self.convert_to_cache(record[self.name] | value, record, validate=False)
            else:
                val = UnionUpdate(self, record, value)
            record._cache[self] = val
    def convert_to_cache(self, value, record, validate=True):