I have identical problem. This is an issue for me, as google drive is the main storage cloud I use for everything, and it works fine for me with all other apps. Would be important for affinity to sort this out.
Here is info I found about this problem online for another app (Clicker / DocsPlus):
“This is an issue with the Google Drive service itself.
There are many ways to upload a file to Google Drive. Depending on the method used, Google Drive may classify a Clicker / DocsPlus file as a different type. This causes the file to appear dimmed and unopenable in our apps.
We've updated our software to reduce the chances of this happening. However, older files may still be affected.”