"Is this a bug or what else can I do?"
"…for example, the colons, but these are displayed with a rectangle as a "placeholder"."
Hi pmfh,
well, yes, this is a bug.
What's your operating system?
One way to resolve the issue could be to store the font files in the Fonts folder of InDesign's Application folder.
In the case of activated Adobe Fonts this cannot happen, because the font files are not accessible on your machine.
As far as I can see the developers are working on a fix, that hopefully should be out soon.
But as of today I currently can only suggest that you join InDesign Prerelease to produce your PDFs with the Prerelease version 17.1.0 of InDesign. Do not try this with the Prerelease 17.7.0 which is shown as the latest prerelease version if you are into InDesign Prerelease.
How to join InDesign Prerelease:
https://www.adobeprerelease.com/beta/C6DFA254-C40C-4EEB-8F6D-F4AEDA2E6171
More on Adobe Prerelease programs:
How to Join Creative Cloud Prerelease Programs
Erin Finnegan, Oct 18, 2019, UPDATE July 24th
https://medium.com/adobetech/how-to-join-creative-cloud-prerelease-programs-ccecc10ae7d3
Below a link to one of my posts where I listed threads that are discussing similar issues.
Hm. I must admit that a glyph not exported and not showing a non-def-glyph glyph is totally new to me.
Blank box over colon when exporting PDF from Indesign
CallMeC, Jan 07, 2022
https://community.adobe.com/t5/indesign-discussions/blank-box-over-colon-when-exporting-pdf-from-indesign/m-p/12640595#M460386
Regards,
Uwe Laubender
( ACP )