Tk-nuke fails due to core.python.tank.pickle.dumps error on diacritics in user name

A user can launch Nuke 13.0.3 via tk-nuke v0.14.1 and Desktop, but the Shotgrid menu is missing. The same launcher works for everyone else.

After some digging it turns out that pickle.dumps in core.python.tank fails with the umlaut in his name.

In [30]: pickle.dumps("ö")
UnicodeDecodeError                        Traceback (most recent call last)
<ipython-input-30-b11ebd35d121> in <module>
----> 1 picklek.dumps("ö")

/projects/SG_CONF/xxx/install/core/python/tank/util/ in dumps(data)
     44     # See
     45     # Decode the result to a str before returning.
---> 46     return six.ensure_str(cPickle.dumps(data, **DUMP_KWARGS))

/projects/SG_CONF/xxx/install/core/python/tank_vendor/ in ensure_str(s, encoding, errors)
    897         s = s.encode(encoding, errors)
    898     elif PY3 and isinstance(s, binary_type):
--> 899         s = s.decode(encoding, errors)
    900     return s

UnicodeDecodeError: 'utf-8' codec can't decode byte 0xf6 in position 1: invalid start byte

This does seem to be the correct unicode code:

Maybe the string was produced in utf-16.