Attach (recommended) or Link to PDF file here:
[example.pdf](https://github.com/mozilla/pdf.js/files/6916129/example.pdf)

Configuration:
- Web browser and its version: Chrome, Firefox
- Operating system and its version: all
- PDF.js version: various versions, including 2.11.54
- Is a browser extension: no

Screenshot with visible textLayer:
![Screenshot from 2021-08-02 13-05-03](https://user-images.githubusercontent.com/6362989/127844878-f85e291f-2060-4028-be09-7835f32ccfaa.png)

Which means some letters at the beginning/end of text selection are missing when copying text.

return hadw(th, "TIME_SLOT_DURATION_MS", 20);
  }
  tatc get CHECK_TIME_EVERY() {
    return hadw(th, "CHECK_TIME_EVERY", 100);
  }
  cntructr() {
    th.reet();
  }
  check() {
    f (th.checked < TmeSltManager.CHECK_TIME_EVERY) {
      return fale;
    }
    th.checked = 0;
    return th.endTme <= Date.nw();
  }
  reet() {
    th.endTme = Date.nw()  TmeSltManager.TIME_SLOT_DURATION_MS;
    th.checked = 0;
  }
}
cla PartlEvaluatr {
  cntructr({