Chinese Characters missing after Adobe Reader Update?

Dear community,

We are facing an issue in some of our PDF interactive documents since about two weeks.
The documents are created from a SAP system and rendered by the SAP Adobe Document Service Server. The documents couldn't be opened by Adobe Reader after updating the SAP ADS Server so we had to update our Adobe Reader (from 25.001.20844 to first 25.001.20918)
Otherwise we get the message "To view the full contents of this document, you need a later version of the PDF viewer. You can upgrade to to the latest version of Adobe Reader from www.adobe...". and so on

But after updating the Adobe Reader and opening our documents (even the ones saved long time before updating the SAP ADS Server (I checked documents from January this year) all chinese characters in this documents are missing - or better explained - they are replaced by boxes.

I found the following community thread: Gelöst: Chinese Character can not display correct after la... - Adobe Product Community - 14010681

And after that we updated our Adobe Reader to the latest available version (25.001.20937) but the issue still exists.

Edge cannot open the documents at all (SAP interactive forms are not supported by SAP in chromium based browsers) so we don't have a workaround at the moment for our chinese colleagues.

Do we have a similar issue with the actual version of Adobe Reader as in the linked community thread? I googled and searched the Adobe site and this community but I didn't find something fitting our version.

This is how the chinese characters look at the moment opening the PDF: