error in scanner: disappearing file?

Got one of those again:

INFO: Scanning source for common problems...
ERROR: Could not build app com.totsp.crossword.shortyz due to unknown error: Traceback (most recent call last):
  File "/home/bubu/projects/oss/fdroidserver/fdroidserver/build.py", line 1101, in main
    if trybuild(app, build, build_dir, output_dir, log_dir,
  File "/home/bubu/projects/oss/fdroidserver/fdroidserver/build.py", line 871, in trybuild
    build_local(app, build, vcs, build_dir, output_dir, log_dir, srclib_dir, extlib_dir, tmp_dir, force, onserver, refresh)
  File "/home/bubu/projects/oss/fdroidserver/fdroidserver/build.py", line 516, in build_local
    count = scanner.scan_source(build_dir, build)
  File "/home/bubu/projects/oss/fdroidserver/fdroidserver/scanner.py", line 319, in scan_source
    if is_binary(filepath) and not safe_path(path_in_build_dir):
  File "/home/bubu/projects/oss/fdroidserver/fdroidserver/scanner.py", line 234, in safe_path
    if imghdr.what(path) is not None:
  File "/usr/lib/python3.8/imghdr.py", line 16, in what
    f = open(file, 'rb')
FileNotFoundError: [Errno 2] No such file or directory: 'puzlib/src/test/resources/2010-7-4-LosAngelesTimes.puz'

The file does exist