Problem with Preview Pane

System information: [ Citavi Version 5.2, Windows 10, English, Google Chrome, MS Office 2016, - ]
Hello,
I can no longer see any of my reference documents in the preview pane (see image below, may have to open in new tab to see the whole image). None of the view button commands seem to be working either. I have tried zooming (in/out), "fit to" and "show next". Nothing seems to be working. Has anyone else come across this before?

Thank you,
Brian
Hello,
I can no longer see any of my reference documents in the preview pane (see image below, may have to open in new tab to see the whole image). None of the view button commands seem to be working either. I have tried zooming (in/out), "fit to" and "show next". Nothing seems to be working. Has anyone else come across this before?
Thank you,
Brian