I’m using DTTG 2.7.6 on an iPad Pro 10.5" on iOS 13.3. I am experiencing a bug that prevents me from seeing the Thumbnail view of a PDF. If I load a PDF and select the Thumbnail button (top-right, four squares), it works as expected. But if I switch to another app and return to DTTG with an active document selected, and then select the Thumbnail button, nothing happens. The only way to clear the bug is to close the PDF and re-open it.
Thanks for the report! Confirmed and filing an issue. Thanks for your patience and understanding.