Strange pyparsing error

[white-gecko]

Sometimes this query results in the following error (the default-graph-uri is set as you can see in the log).

select distinct ?class { {?s a ?class} union {?class a <http://www.w3.org/2000/01/rdf-schema#Class>} union {?class a <http://www.w3.org/2002/07/owl#Class>} } order by ?class

::ffff:127.0.0.1 - - [01/Sep/2019 18:25:17] "POST /sparql HTTP/1.1" 500 -
::ffff:127.0.0.1 - - [01/Sep/2019 18:25:18] "OPTIONS /sparql?default-graph-uri=https%3A%2F%2Fmygraphuri%2Fpath%2F HTTP/1.1" 200 -
2019-09-01 18:25:18,253 - quit.modules.endpoint - DEBUG - Request method: POST
2019-09-01 18:25:18,262 - quit - ERROR - Exception on /sparql [POST]
Traceback (most recent call last):
  File "site-packages/flask/app.py", line 2446, in wsgi_app
  File "site-packages/flask/app.py", line 1951, in full_dispatch_request
  File "site-packages/flask_cors/extension.py", line 161, in wrapped_function
  File "site-packages/flask/app.py", line 1820, in handle_user_exception
  File "site-packages/flask/_compat.py", line 39, in reraise
  File "site-packages/flask/app.py", line 1949, in full_dispatch_request
  File "site-packages/flask/app.py", line 1935, in dispatch_request
  File "quit/web/modules/endpoint.py", line 72, in sparql
  File "quit/helpers.py", line 212, in parse_query_type
  File "site-packages/rdflib/plugins/sparql/parser.py", line 1060, in parseQuery
  File "site-packages/pyparsing.py", line 1929, in parseString
  File "site-packages/pyparsing.py", line 1669, in _parseNoCache
  File "site-packages/pyparsing.py", line 4037, in parseImpl
  File "site-packages/pyparsing.py", line 1669, in _parseNoCache
  File "site-packages/pyparsing.py", line 4222, in parseImpl
  File "site-packages/pyparsing.py", line 1669, in _parseNoCache
  File "site-packages/pyparsing.py", line 4430, in parseImpl
  File "site-packages/pyparsing.py", line 1669, in _parseNoCache
  File "site-packages/pyparsing.py", line 4037, in parseImpl
  File "site-packages/pyparsing.py", line 1669, in _parseNoCache
  File "site-packages/pyparsing.py", line 4817, in parseImpl
  File "site-packages/pyparsing.py", line 1669, in _parseNoCache
  File "site-packages/pyparsing.py", line 4430, in parseImpl
  File "site-packages/pyparsing.py", line 1669, in _parseNoCache
  File "site-packages/pyparsing.py", line 4430, in parseImpl
  File "site-packages/pyparsing.py", line 1669, in _parseNoCache
  File "site-packages/pyparsing.py", line 4037, in parseImpl
  File "site-packages/pyparsing.py", line 1669, in _parseNoCache
  File "site-packages/pyparsing.py", line 4665, in parseImpl
  File "site-packages/pyparsing.py", line 1669, in _parseNoCache
  File "site-packages/pyparsing.py", line 4430, in parseImpl
  File "site-packages/pyparsing.py", line 1669, in _parseNoCache
  File "site-packages/pyparsing.py", line 4430, in parseImpl
  File "site-packages/pyparsing.py", line 1669, in _parseNoCache
  File "site-packages/pyparsing.py", line 4222, in parseImpl
  File "site-packages/pyparsing.py", line 1702, in _parseNoCache
  File "site-packages/pyparsing.py", line 1308, in wrapper
TypeError: postParse2() missing 1 required positional argument: 'tokenList'

unfortunately it is not simple to reproduce this issue, as it does not happen on every start of the store. So far I've only experienced this issue using the pyinstaller binaries, on MacOS and on Linux.