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I forgot to ask if you are also using Google Drive as a separate Android app.
I checked the Adobe Scan app and it doesn't have any settings that control metered connections on its own but the Google Drive app does.
And altgough Adobe Scan app does have hidden permissions to access WiFi or the cellular data networks, the app itself doesn't have a modifiable setting that can interfere with the behavior that you've observed, but the Google Drive app does.
This issue is not from the Adobe Scan app.
You've asked a question in the Adobe Scan support forum that pertains to a feature of the Google Drive app and it could've been answered for you in the Google Drive support forums.
But anyway, with your Google Drive app opened go to settings and disable "Transfer files only over Wi-Fi".