On 7.0.0-beta.65+b047f3d90 on a win10 machine

When trying to open multiple PDF files from Zotero only the first double-clicked (or right click > open PDF) item is opened in the external PDF program. The second file only opens after the first instance of the external reader is closed. Likewise, the third file only opens when the second is closed, etc. (If I click 10 files, these will all "wait" in line to be opened and closed consecutively).

Because this happens with multiple PDF programs (I tried Acrobat and Foxit) and opening the same files directly from explorer works as expected (that is, multiple instances of the same program or multiple tabs are opened - depending on program-specific preferences), I'm inclined to think the problem lies with Zotero.

The problem does not occur using Zotero's built-in PDF reader.

(edit) Additional observation: if the first tab of the external PDF reader is opened via a file in explorer, additional PDF files can be opened in tabbed view without problem through zotero. Again, this applies to both programs.