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).


try:
            return value.float_repr()         
        except Exception:
            return float(value or 0.0)
    def convert_to_cache(self, value, record, validate=True):
        if validate:
            currency = record[self.currency_field]
            
            
            if currency:
                value = currency.round(float(value or 0.0))
                return float_precision(value, currency.decimal_places)
        return float(value or 0.0)
    def convert_to_read(self, value, record, use_name_get=True):
        
        return float(value)
    def convert_to_write(self, value, record):
        return value
class _String(Field):
    """ Abstract class for string fields. """
    _slots = {
        'translate': False,             
    }
    def __init__(self, string=Default, **kwargs):