Why do my tif images not show up?

There currently is a drupal bug: If you have your images in the public files directory without any subdirectory (what we all usually do have...) and if you have a convert command in your image style (e.g. convert to jpg - which we all usually do have) then you currently need a patch:

https://www.drupal.org/files/issues/2018-10-04/2630230.patch

apply in your drupal root with

patch -p1 < 2630230.patch

see https://www.drupal.org/project/drupal/issues/2630230