Exception raised by tbwiki software

Traceback (most recent call last):
  File "/home2/birdorg/public_html/cgi-bin/tbwiki.cgi", line 55, in 
    main(req)
  File "/home2/birdorg/work/tbwiki/cgi-bin/tbwiki_engine.py", line 2771, in main
    html = re.sub(highlight, new_str, html)
  File "/usr/lib64/python3.9/re.py", line 210, in sub
    return _compile(pattern, flags).sub(repl, string, count)
  File "/usr/lib64/python3.9/re.py", line 304, in _compile
    p = sre_compile.compile(pattern, flags)
  File "/usr/lib64/python3.9/sre_compile.py", line 788, in compile
    p = sre_parse.parse(p, flags)
  File "/usr/lib64/python3.9/sre_parse.py", line 955, in parse
    p = _parse_sub(source, state, flags & SRE_FLAG_VERBOSE, 0)
  File "/usr/lib64/python3.9/sre_parse.py", line 444, in _parse_sub
    itemsappend(_parse(source, state, verbose, nested + 1,
  File "/usr/lib64/python3.9/sre_parse.py", line 843, in _parse
    raise source.error("missing ), unterminated subpattern",
re.error: missing ), unterminated subpattern at position 28