Octolapse failing with cryptic error about file line numbers

I'm using octolapse version 0.4.1 (release), and when I start the print job from OctoPod (iOS version), octolapse fail with the cryptic error:

2022-07-26 12:33:22,508 - octolapse.timelapse - ERROR - File line number 2 was expected, but 2 was received!

and fails to initialize.

This message seems to arise from this line 1380 in timelapse.py:

    def check_current_line_number(self, tags):
        # check the current line number
        if 'source:file' in tags:
            # this line is from the file, advance!
            self._current_file_line += 1
            if "fileline:{0}".format(self._current_file_line) not in tags:
                actual_file_line = "unknown"
                for tag in tags:
                    if len(tag) > 9 and tag.startswith("fileline:"):
                        actual_file_line = tag[9:]
                message = "File line number {0} was expected, but {1} was received!".format(
                    self._current_file_line + 1,
                self.stop_snapshots(message, True)

So this would seem to indicate that the tag with fileline:2 is corrupted somehow. Anybody know what might be causing this?