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 decimal precision and currency symbol are taken from the attribute
    :param currency_field: name of the field holding the currency this monetary
                           field is expressed in (default: `currency_id`)
    """
    type = 'monetary'
    column_type = ('numeric', 'numeric')
    _slots = {
        'currency_field': None,
        'group_operator': 'sum',
    }
    def __init__(self, string=Default, currency_field=Default, **kwargs):
        super(Monetary, self).__init__(string=string, currency_field=currency_field, **kwargs)
    _related_currency_field = property(attrgetter('currency_field'))
    _description_currency_field = property(attrgetter('currency_field'))
    _description_group_operator = property(attrgetter('group_operator'))
    def _setup_regular_full(self, model):
        super(Monetary, self)._setup_regular_full(model)
        if not self.currency_field:
            
            if 'currency_id' in model._fields:
                self.currency_field = 'currency_id'
            elif 'x_currency_id' in model._fields:
                self.currency_field = 'x_currency_id'
        assert self.currency_field in model._fields, \
            "Field %s with unknown currency_field %r" % (self, self.currency_field)
    def convert_to_column(self, value, record):