What I've found is that the following conditions are mandatory to
reproduce the error :
- Use a build for Windows (There is no problem on my Gnu/Linux 
  platform)
- Use a version of modus past f76fc911 where the :height property 
  was
added to the fill-column-indicator face.
- Use hs-minor-mode and hide all regions

On my Gnu/Linux (see Screenshot_20220327_183833.png) there is no 
problems to reach the end of buffer.