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
"""Returns the given timestamp converted to the client's timezone.
           This method is *not* meant for use as a default initializer,
           because datetime fields are automatically converted upon
           display on client side. For default values :meth:`fields.datetime.now`
           should be used instead.
           :param datetime timestamp: naive datetime value (expressed in UTC)
                                      to be converted to the client timezone
           :rtype: datetime
           :return: timestamp converted to timezone-aware datetime in context
                    timezone
        """
        assert isinstance(timestamp, datetime), 'Datetime instance expected'
        tz_name = record._context.get('tz') or record.env.user.tz
        utc_timestamp = pytz.utc.localize(timestamp, is_dst=False)  
        if tz_name:
            try:
                context_tz = pytz.timezone(tz_name)
                return utc_timestamp.astimezone(context_tz)
            except Exception:
                _logger.debug("failed to compute context/client-specific timestamp, "
                              "using the UTC value",
                              exc_info=True)
        return utc_timestamp
    @staticmethod
    def from_string(value):