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).


if callable(self._digits):
            with LazyCursor() as cr:
                return self._digits(cr)
        else:
            return self._digits
    _related__digits = property(attrgetter('_digits'))
    _description_digits = property(attrgetter('digits'))
    _description_group_operator = property(attrgetter('group_operator'))
    def convert_to_column(self, value, record):
        result = float(value or 0.0)
        digits = self.digits
        if digits:
            precision, scale = digits
            result = float_repr(float_round(result, precision_digits=scale), precision_digits=scale)
        return result
    def convert_to_cache(self, value, record, validate=True):
        
        value = float(value or 0.0)
        if not validate:
            return value
        digits = self.digits
        return float_round(value, precision_digits=digits[1]) if digits else value
    def convert_to_export(self, value, record):
        if value or value == 0.0:
            return value if record._context.get('export_raw_data') else ustr(value)
        return ''
class Monetary(Field):