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
""" High-level objects for fields. """
from collections import OrderedDict, defaultdict
from datetime import date, datetime
from functools import partial
from operator import attrgetter
from types import NoneType
import json
import logging
import pytz
import xmlrpclib
import psycopg2
from odoo.sql_db import LazyCursor
from odoo.tools import float_precision, float_repr, float_round, frozendict, \
                       html_sanitize, human_size, pg_varchar, ustr, OrderedSet
from odoo.tools import DEFAULT_SERVER_DATE_FORMAT as DATE_FORMAT
from odoo.tools import DEFAULT_SERVER_DATETIME_FORMAT as DATETIME_FORMAT
from odoo.tools.translate import html_translate, _
DATE_LENGTH = len(date.today().strftime(DATE_FORMAT))
DATETIME_LENGTH = len(datetime.now().strftime(DATETIME_FORMAT))
EMPTY_DICT = frozendict()
RENAMED_ATTRS = [('select', 'index'), ('digits_compute', 'digits')]
_logger = logging.getLogger(__name__)
_schema = logging.getLogger(__name__[:-7] + '.schema')
Default = object()                      
class SpecialValue(object):