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
""" 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):