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).


""" The precision digits are given by the attribute
    :param digits: a pair (total, decimal), or a function taking a database
                   cursor and returning a pair (total, decimal)
    """
    type = 'float'
    _slots = {
        '_digits': None,                
        'group_operator': 'sum',
    }
    def __init__(self, string=Default, digits=Default, **kwargs):
        super(Float, self).__init__(string=string, _digits=digits, **kwargs)
    @property
    def column_type(self):
        
        
        
        
        
        return ('numeric', 'numeric') if self.digits is not None else \
               ('float8', 'double precision')
    @property
    def digits(self):